
Class _ ' 

Rnok '■■■ - V 



TWENTIETH CENTURY TEXT-BOOKS 

EDITED BY 

A. F. NIGHTINGALE, Ph.D., LL.D. 

SUPERINTENDENT OF SCHOOLS, COOK COUNTY, ILLINOIS 



TWENTIETH CENTURY TEXT-BOOKS. 



ZOOLOGY. 

ANIMAL STUDIES. A one-book course in 
Zoology for secondary schools. By David 
Starr Jordan, President of Leland Stanford 
Jr. University ; Vernon L. Kellogg, M.S., 
Professor of Entomology, Leland Stanford Jr. 
University ; and Harold Heatti, Professor 
of Zoology, Leland Stanford Jr. University. 
Cloth, $1.25 net. 

ANIMAL LIFE. A First Book of Zoology. 
By David Starr Jordan and Vernon L. 
Kellogg. Cloth, $1.20 net. 

ANIMAL FORMS. An Elementary Text-Book 
of Zoology. By David Starr Jordan and 
Harold Heath. Cloth, $1.10 net. 

ANIMALS. A Text-Book of Zoology. By 
Jordan, Kellogg, and Heath. (The two 
foregoing in one volume.) Cloth. $1.80 net. 

Teacher's Manuals. 

ANIMAL STRUCTURES. A Laboratory 
Manual of Zoology. By D. S. Jordan and 
George C. Price, Associate Professor of Zo- 
ology, Leland Stanford Jr. University. Limp 
cloth, 50 cents net. 



D. APPLETON AND COMPANY, NEW YORK. 



TWENTIETH CENTURY TEXT-BOOKS 



ANIMAL STUDIES 



A TEXT- BOOK OF ELEMENTARY ZOOLOGY 
FOR USE IN HIGH SCHOOLS AND COLLEGES 



BY 

DAVID STARR JORDAN 

PRESIDENT OF LELAND STANFORD JR. UNIVERSITY 

VERNON LYMAN KELLOGG 

PROFESSOR OF ENTOMOLOGY 
AND 

. HAROLD HEATH 

ASSOCIATE PROFESSOR OF INVERTEBRATE ZOOLOGY 
IN LELAND STANFORD JR. UNIVERSITY 




NEW YORK 
D. APPLETON AND COMPANY 



•J?4 

190 3 a, 



COPYRIGHT, 1903 

By D. APPLETON AND COMPAN1 



Animal Life . . ' ' 

Copyright 1900 by D. Appleton and Company 

Animal Forms 
Copyright 1902 by D. Appleton and Company 



EDITOR'S PREFACE 



The publishers are assured from the most expert testi- 
mony that they are presenting to the educational public, in 
this volume, a compact but complete treatment of elemen- 
tary zoology, especially for those institutions of learning 
which prefer to find in a single book an ecological as well 
as a morphological survey of the animal world. Animal 
Life, in the series, treats largely of ecology, Animal Forms 
of morphology, in this volume the same authors present 
the salient features of each of the above-named books, with 
entirely new and additional chapters on Classification, the 
Economic Value,' and the Ancient History of Animals. In 
Animal Studies an important advance step is taken toward 
meeting the demand for an elementary zoology that shall 
treat of the natural history rather than merely of the mor- 
phology of animals. Several new plates not found in the 
other volumes have been added. The structure, life habits, 
environments, economics, and history of fossil animals are 
each treated with that clearness, conciseness, and complete- 
ness for which President Jordan is particularly distin- 
guished. While the book contains adequate material for a 
year's work, it is also admirably adapted for those schools 
that find it necessary to give a shorter time to this subject. 
The following ideas expressed b-y Dr. Coulter concerning 



VI ANIMAL STUDIES 

the purpose of Plant Studies are entirely applicable to Ani- 
mal Studies as well : 

" The book is intended to serve as a supplement to 
three important factors : 

" (1) The teacher, who must amplify and suggest 
at every point; (2) the laboratory, which must bring 
the pupil face to face with plants and their structures ; 
(3) field-work, which must relate the facts observed in the 
laboratory to their actual place in Xature, and must bring 
new facts to notice which can be observed nowhere else." 

Jordan and Price's Animal Structures, a Laboratory 
Manual of Zoology, will be found eminently useful in con- 
nection with the reading and study of this text. 



CONTENTS 



CHAPTER 

I. — Conditions of animal life . 
^11. —Principles of classification 
4III. — The simplest animals or protozoa 
^IV. — The slightly complex animals or sponges 
*V. — The coslenterates .... 
VI. — The worms . . . 
"VII. — Animals of uncertain relationships 

VlII. — Mollusks 

■OlIX. — The arthropods 

X"K. — Arthropods {continued) class insects 
XI. — Arthropods {continued) class arachnida 

XII. — ECHINODERMS 

XIII. — The chord ates . 
XIV.— The fishes . 
XV. — The amphibians . 
XVI. — The reptiles 
XVII.— The birds . 
XVIII. — The mammals 
*§£IX. — The life cycle . 
XX. — The crowds of animals 



the struggle 



EXISTENCE . 

* XXI.— Adaptations 

/XXII. — Animal communities and social life . 

I/XXIII. — COMMENSALISM AND PARASITISM . 

^XXIV. — Protective resemblances and mimicry 



PAGE 
1 

13 
22 

33 
43 
59 
83 
89 
109 
130 
143 
150 
161 
164 
182 
192 
209 
232 
254 

281 
290 
314 
335 
350 



vm 



ANIMAL STUDIES 



CHAPTER 

u(£_XV. — The special senses .... 
X XXVI.— Instinct and reason 
XXVII. — Economic zoology ... 
XXVIII. — The animals of the past . 

XXIX. — Geographical distribution of animalp 



PAGE 

371 
387 
404 
417 
435 



ANIMAL STUDIES 



CHAPTER I 

CONDITIONS OF ANIMAL LIFE 

1. Divisions of the subject.— Biology is the science which 
treats of living things in all their relations. It is sub- 
divided into Zoology, the science which deals with animals, 
and Botany, which is concerned with plants. The field 
covered by each of these branches is very extensive. 
Within the scope of zoology are included all subjects bear- 
ing on the form and structure of animals, on their develop- 
ment, and on their activities, including the consideration 
of their habits and the wider problems of their distribution 
and their relations to one another. 

These various subjects are often conveniently grouped 
under three heads : Morphology, which treats of the form 
and structure or the anatomy of organisms ; Physiology, 
which considers their activities ; and Ecology, which in- 
cludes their relations one to another and to their surround- 
ings. All the phases of plant or animal existence may be 
considered under one or another of these three divisions. 

2. Difference between animals and plants. — It is easy to 
distinguish between the animal and plant when a butterfly 
is fluttering about a blossoming cherry tree or a cow feed- 
ing in a field of clover. It is not so easy, if it is, indeed, 
possible, to say which is plant and which is animal when 
the simplest plants are compared with the simplest ani- 
mals. It is almost impossible to so define animals as to 

1 



2 ANIMAL STUDIES 

distinguish all of them from all plants, or so to define 
plants as to distinguish all of them from all animals. 
While most animals have the power of locomotion, some, 
like the sponges and polyps and barnacles and numerous 
parasites, are fixed. While most plants are fixed, some of 
the low aquatic forms have the power of spontaneous loco- 
motion, and all plants have some power of motion, as espe- 
cially exemplified in the revolution of the apex of the 
growing stem and root, and the spiral twisting of tendrils, 
and in the sudden closing of the leaves of the sensitive 
plant when touched. Among the green or chlorophyll- 
bearing plants the food consists chiefly of inorganic sub- 
stances, especially of carbon which is taken from the car- 
bonic-acid gas in the atmosphere, and of water. But some 
green-leaved plants feed also in part on organic food. 
Such are the pitcher-plants and sun-dews, and Venus-fly- 
traps, which catch insects and use them for food nutrition. 
But there are many plants, the fungi, which are not green 
— that is, which do not possess chlorophyll, the substance 
on which seems to depend the power to make organic 
matter out of inorganic substances. These plants feed on 
organic matter as animals do. The cells of plants (in their 
young stages, at least) have a wall composed of a peculiar 
carbohydrate substance called cellulose, and this cellulose 
was for a long time believed not to occur in the body of 
animals. But now it is known that certain sea-squirts 
(Tunicata) possess cellulose. It is impossible to find any 
set of characteristics, or even any one characteristic, which 
is possessed only by plants or only by animals. But nearly 
all of the many- celled plants and animals may be easily 
distinguished by their general characteristics. The power 
of breaking up carbonic-acid gas into carbon and oxygen 
and assimilating the carbon thus obtained, the presence of 
chlorophyll, and the cell walls formed of cellulose, are char- 
acteristics constant in all typical plants. In addition, the 
fixed life of plants, and their general use of inorganic sub- 



UUNmTlOJNS OF ANIMAL LIFE 3 

stances for food instead of organic, are characteristics 
readily observed and practically characteristic of many- 
celled plants. When the thousands of kinds of one-celled 
organisms are compared, however, it is often a matter of 
great difficulty or of real impossibility to say whether a 
given organism should be assigned to the plant kingdom 
or to the animal kingdom. In general the distinctive 
characters of plants are grouped around the loss of the 
power of locomotion and related to or dependent upon it. 

3. Living organic matter and inorganic matter. — It would 
seem to be an easy matter to distinguish an organism — that 
is, a living animal or plant — from an inorganic substance. 
It is easy to distinguish a dove or a sunflower from stone, 
and practically there never is any difficulty in making such 
distinctions. But when we try to define living organic mat- 
ter, and to describe those characteristics which are peculiar 
to it, which absolutely distinguish it from inorganic matter, 
we meet with some difficulties. At least many of the char- 
acteristics commonly ascribed to organisms, as peculiar to 
them, are not so. The possession of organs, or the composi- 
tion of the body of distinct parts, each with a distinct func- 
tion, but all working together, and depending on each other, 
is as true of a steam-engine as of a horse. That the work 
done by the steam-engine depends upon fuel is true ; but 
so it is that the work done by the horse depends upon fuel, 
or food as we call it in the case of the animal. The oxida- 
tion or burning of this fuel in the engine is wholly compar- 
able with the oxidation of the food, or the muscle and fat 
it is turned into, in the horse's body. The composition of 
the bodies of animals and plants of tiny structural units, 
the cells, is in many ways comparable with the composition 
of some rocks of tiny structural units, the crystals. But 
not to carry such rather quibbling comparisons too far, it 
may be said that organisms are distinguished from inorganic 
substances by the following characteristics : Organization ; 
the power to make over inorganic substances into organic 



4 ANIMAL STUDIES 

matter, or the changing of organic matter of one kind, as 
plant matter, into another kind, as animal matter ; motion, 
the power of spontaneous movement in response to stimuli ; 
sensation, the power of being sensible of external stimuli ; 
reproduction, the power of producing new beings like them- 
selves ; and adaptation, the power of responding to external 
conditions in a way useful to the organism. Through adap- 
tation organisms continue to exist despite the changing of 
conditions. If the conditions surrounding an inorganic 
body change, even gradually, the inorganic body does not 
change to adapt itself to these conditions, but resists them 
until no longer able to do so, when it loses its identity. 

4. Primary conditions of animal life.— Certain primary 
conditions are necessary for the existence of all animals. 
We know that fishes can not live very long out of water,, 
and that birds can not live in water. These, however, are 
special conditions which depend on the special structure 
and habits of these two particular kinds of backboned ani- 
mals. But the necessity of a constant and sufficient sup- 
ply of air is a necessity common to both ; it is one of the 
primary conditions of their life. All animals must have 
air. Similarly both fishes and birds, and all other animals 
as well, must have food. This is another one of the pri- 
mary conditions of animal life. That backboned animals 
must find somehow a supply of salts or compounds of lime 
to form into bones is a special condition peculiar to these 
animals. 

5. Food. — All the higher plant?, those that are green 
(chlorophyll-bearing), can make their living substance out 
of inorganic matter alone — that is, use inorganic substances 
as food. But animals can not do this. They must have 
already formed organic matter for food. This organic mat- 
ter maybe the living or dead tissues of plants, or the living 
or dead tissues of animals. For the life of animals it is 
necessary that other organisms live, or have lived. It is 
this need which primarily distinguishes an animal from a 



CONDITIONS OF ANIMAL LIFE 5 

plant. Animals can not exist without plants. The plants 
furnish all animals with food, either directly or indirectly. 
The amount of food and the kinds of food required by 
various kinds of animals are special conditions depending 
on the size, the degree of activity, the structural character 
of the body, etc., of the animal in question. Those which 
do the most need most. Those with warmest blood, great- 
est activity, and most rapid change of tissues are most 
dependent on abundance, regularity, and fitness of their 
food. As we well know, an animal can live for a longer or 
shorter time without food. Men have fasted for a month, 
or even two months. Among cold-blooded animals, like the 
reptiles, the general habit of food taking is that of an occa- 
sional gorging, succeeded by a long period of abstinence. 
Many of the lower animals can go without food for surpris- 
ingly long periods without loss of life. But the continued 
lack of food results inevitably in death. Any animal may 
be starved in time. 

If water be held not to be included in the general con- 
ception of food, then special mention must be made of the 
necessity of water as one of the primary conditions of ani- 
mal life. Protoplasm, the basis of life, is a fluid, although 
thick and viscous. To be fluid its components must be 
dissolved or suspended in water. In fact, all the truly 
living substance in an animal's body contains water. The 
water necessary for the animal may be derived from the 
other food, all of which contains water in greater or 
less quantity, or may be taken apart from the other 
food, by drinking or by absorption through the skin. 
Sheep are seldom seen to drink, for they find almost 
enough water in their green food. Fur seals never drink, 
for they absorb the water needed through pores in the 
skin. 

6. Oxygen. — Animals must have air in order to live, 
but the essential element of the air which they need is its 
oxygen. For the metabolism of the body, for the chemical 



6 ANIMAL STUDIES 

changes which take place in the body of every living ani- 
mal, a supply of oxygen is required. This oxygen is de- 
rived directly or indirectly from the air. The atmosphere 
of the earth is composed of 79.02 parts of nitrogen (includ- 
ing argon), .03 parts of carbonic acid, and 20.95 parts of 
oxygen. Thus all the animals which live on land are en- 
veloped by a substance containing nearly 21 per cent of 
oxygen. But animals can live in an atmosphere containing 
much less oxygen. Certain mammals, experimented on, 
lived without difficulty in an atmosphere containing only 
14 per cent of oxygen ; when the oxygen was reduced to 7 
per cent serious disturbances were caused in the animal's 
condition, and death by suffocation ensued when 3 per 
cent of oxygen was left in the atmosphere. Animals which 
live in water get their oxygen, not from the water itself 
(water being composed of hydrogen and oxygen), but from 
air which is mechanically mixed with the water. Fishes 
breathe the air which is mixed with or dissolved in the 
water. This scanty supply therefore constitutes their at- 
mosphere, for in water from which all air is excluded no 
animal can breathe. Whatever the habits of life of the 
animal, whether it lives on the land, in the ground, or in 
the water, it must have oxygen or die. 

7. Temperature, pressure, and other conditions. — Some 
physiologists include among the primary or essential gen- 
eral conditions of animal life such conditions as favorable 
temperature and favorable pressure. It is known from ob- 
servation and experiment that animals die when a too low 
or a too high temperature prevails. The minimum or 
maximum of temperature between which limits an animal 
can live varies much among different kinds of animals. It 
is familiar knowledge that many kinds of animals can be 
frozen and yet not be killed. Insects and other small ani- 
mals may lie frozen through a winter and resume active 
life again in the spring. An experimenter kept certain 
fish frozen in blocks of ice at a temperature of —15° C. 



CONDITIONS OF ANIMAL LIFE 7 

for some time and then gradually thawed them out un- 
hurt. Only very hardy kinds adapted to the cold would, 
however, survive such treatment. There is no doubt that 
every part of the body, all of the living substance, of these 
fish was frozen, for specimens at this temperature could be 
broken and pounded up into fine ice powder. But a tem- 
perature of —20° C. killed the fish. Frogs lived after being 
kept at a temperature of —28° C, centipedes at —50° C, and 
certain snails endured a temperature of —120° C. without 
dying. At the other extreme, instances are known of ani- 
mals living in water (hot springs or water gradually heated 
with the organisms in it) of a temperature as high as 50° C. 
Experiments with Amcehce show that these simplest animals 
contract and cease active motion at 35° C, but are not killed 
until a temperature of 40° to 45° C. is reached. 

The pressure or weight of the atmosphere on the sur- 
face of the earth is nearly fifteen pounds on each square 
inch. This pressure is exerted equally in all directions, so 
that an object on the earth's surface sustains a pressure on 
each square inch of its surface exposed to the air of fifteen 
pounds. Thus all animals living on the earth's surface or 
near it, live under this pressure, and know no other condi- 
tion. For this reason they do not notice it. The animals 
that live in water, however, sustain a much greater pres- 
sure, this pressure increasing with the depth. Certain 
ocean fishes live habitually at great depths, as two to five 
miles, where the pressure is equivalent to that of many 
hundred atmospheres. If these fishes are brought to the 
surface their eyes bulge out fearfully, being pushed out 
through reduced expansion ; their scales fall off because of 
the great expansion of the skin, and the stomach is pushed 
out from the mouth till it is wrong side out. Indeed, the 
bodies sometimes burst. Their bodies are accustomed to 
this great pressure, and when this outside pressure is sud- 
denly removed the body may be bursted. Sometimes such 
a fish is raised from its proper level by a struggle with its 



8 ANIMAL STUDIES 

prey, when both captor and victim may be destroyed by 
the expansion of the body. Some fishes die on being taken 
out of water through the swelling of the air bladder and 
the bursting of its blood-vessels. If an animal which lives 
normally on the surface of the earth is taken up a very high 
mountain or is carried up in a balloon to a great altitude 
where the pressure of the atmosphere is much less than it 
is at the earth's surface, serious cousequences may ensue, 
and if too high an altitude is reached death occurs. This 
death may be in part due to the difficulty in breathing in 
sufficient oxygen to maintain life,. but it is probably chiefly 
due to the disturbances caused by the removal of the pres- 
sure to which the body is accustomed and is structurally 
adapted to withstand. All living animals are accustomed 
to live under a certain pressure, and there are evidently 
limits of maximum or minimum pressure beyond which no 
animal at present existing can go and remain alive. 

But in the case both of temperature and pressure con- 
ditions it is easy to conceive that animals might exist which 
could live under temperature and pressure conditions not 
included between the minimum and maximum limits of each 
as determined by animals so existing. But it is impossible 
to conceive of animals which could live without oxygen or 
without organic food. The necessities of oxygen and organic 
food (and water) are the primary or essential conditions for 
the existence of any animals. 

Of course, we might include such conditions, among 
the primary conditions, as the light and heat of the sun, 
the action of gravitation, and other physical conditions, 
without which existence or life of any kind would be im- 
possible on this earth. But we here consider by "primary 
conditions of animal life" rather those necessities of 
living animals as opposed to the necessities of living 
plants. Neither animals nor plants could exist without 
the sun, whence they derive directly or indirectly all their 
energy. 



CONDITIONS OF ANIMAL LIFE 9 

8. Cells. — If we examine very carefully the different parts 
of some highly developed animal under the high powers of 
the microscope we find that they are composed of a multi- 
tude of small structures which bear the same relations to 
the various organs that bricks or stones do to a wall ; and 
if the investigation were continued it would be found that 
every organism is composed of one or more of these lesser 
elements which bear the name of cells. In size they vary 
exceedingly, and their shapes are most diverse, but, despite 
these differences, it will be seen that all exhibit a certain 
general resemblance one to the other. 

9. Shape of cells. — In many of the simpler organisms the 
component cells are jelly-like masses of a more or less 
spherical form, but as we ascend the scale of life the condi- 
tion of affairs becomes much more complex. In the mus- 
cles the cells are long and slender (Fig. 1, D) ; those form- 
ing the nerves and conveying sensations to and from all 
parts of the body, like an extensive telegraph system, are 
excessively delicate and thread-like ; in the skin, and lining 
many cavities of the body, where the cells are united into 
extensive sheets, they range in shape from high and colum- 
nar to flat and scale-like forms (Fig. 1, E, E, G). The cells 
of the blood present another type (Fig. 1, B) ; and so we 
might pass in review other parts of the body, and con- 
tinue our studies with other groups of animals, always find- 
ing new forms dependent upon the part they play in the 
organism. 

10. Size of cells. — Also in the matter of size the greatest 
variations exist. Some of the smallest cells measure less 
than one micromillimeter ( 8 gSoo of an inch) in diameter. 
Over five hundred million such bodies could be readily 
stowed away into a hollow sphere the size of the letter be- 
ginning this sentence. In a drop of human blood of the 
same size, between four and five million blood-cells or cor- 
puscles float. And from this extreme all sizes exist up to 
those with a diameter of 2.5 or 5 cm. (one or two inches), 

2 



10 ANIMAL STUDIES 

as in the case of the hen's or ostrich's egg. On the average 
a cell will measure between .025 to .031 mm. (^ and 
rta- of an inch) in diameter, a speck probably invisible to 
the unaided eye. While the size and external appearance 
of a cell are seen to be most variable, the internal structures 
are found to show a striking resemblance throughout. All 
are constructed upon essentially the same plan. Differ- 
ences in form and size are superficial, and in passing to a 
more careful study of one cell we gain a knowledge of the 
important features of all. 

11. A typical cell.— An egg-cell (Fig. 1, A) or some sim- 
ple one from the liver or skin may be chosen as a good rep- 
resentative of a typical cell. To the naked eye it is barely 
visible as a minute speck ; but under the microscope the 
appearance is that of so much white of egg, an almost trans- 
parent jelly-like mass bearing upon its outer surface a thin 
structureless membrane that serves to preserve its general 
shape and also to protect the delicate cell material within. 
The comparison of the latter substance to egg albumen can 
be carried no further than the simple physical appearance, 
for albumen belongs to that great class of substances which 
are said to be non-living or dead, while the cell material 
or protoplasm, as it is termed, is a living substance. We 
know of no case where life exists apart from protoplasm, 
and for this reason the latter is frequently termed the 
physical basis of life. 

In addition to the features already described, the proto- 
plasm of every perfect cell is modified upon the interior to 
form a well-defined spherical mass known as the nucleus. 
Other structures are known to occur in the typical cell. 
Experiment shows that the nucleus and cell protoplasm are 
absolutely indispensable, whatever their size and shape, and 
therefore we are at present justified in defining the cell as 
a small mass of protoplasm enclosing a nucleus. 

12. Structure of protoplasm. — When seen under a glass 
of moderate power protoplasm gives no indication of any 



CONDITIONS OF ANIMAL LIFE 



11 



definite structure, and even with the highest magnification 
it presents appearances which are not clearly understood. 
According to the commonly accepted view, it consists of 
two portions, one, the firmer, forming an excessively delicate 




J— !^> 



Fig. 1. — Different types of cells composing the body of a highly developed animal. 
A, cell ; f, food materials ; n, nucleus, B, blood-cell. C, nerve-cell with small 
part of its fiber. D, muscle fiber. E, cells lining the body cavity. F, lining of 
the windpipe. G, section through the skin. Highly magnified. 

meshwork (Fig. 1, A) enclosing in its cavities the second 
more fluid part. Therefore, when highly magnified, the 
appearance would he essentially like a sponge fully satu- 
rated with water ; but it should be remembered that in the 
protoplasm the sponge work, and possibly the fluid part, is 
living, and that both are transparent. 

There are reasons for thinking that the structure and 



12 ANIMAL STUDIES 

the composition of protoplasm may change somewhat under 
certain circumstances. It certainly is not everywhere alike, 
for that of one animal must differ from that of another, and 
different parts, such as the liver and brain, of the same form 
must be unlike. These differences, however, are minor 
when compared to the resemblances, for, as we shall see, 
this living substance, wherever it exists, carries on the pro- 
cesses of waste, repair, growth, sensation, contraction, and 
the reproduction of its kind. 

13. Animal functions. — Animals in general lead active, 
busy lives, collecting food, avoiding enemies, and producing 
and caring for their young. While the activities of all 
animals are directed to their own preservation and to the 
multiplication of their kind, these processes are carried on 
in the most diverse ways. The manner in which an organ 
or an organism is made, and the method by which it does 
its work, are mutually dependent one on the other. As 
there is an enormous number of species of animals, each 
differently constructed, there is, accordingly, a very great 
variety of habits. As we shall see, the lower forms are 
remarkably simple in their construction, and their mode of 
existence is correspondingly simple. In the higher t}*pes 
a much greater complexity exists, and their activities are 
more varied and are characterized by a high degree of elabo- 
ration. In every case, the animal, whether high or low, is 
fitted for some particular haunt, where it may perform its 
work in its own special way and may lead a successful life 
of its own characteristic type. 



CHAPTER II 

PRINCIPLES OF CLASSIFICATION 

14. Classification. — It is plain that natural relations of 
dome sort exist among living organisms. A dog is more 
like a' cat than it is like a sheep. A dog is more like a 
sheep than either is like a butterfly. The very existence 
of such terms as animals and plants, insects and fishes, 
implies various grades of relationship. Classification is the 
process of reducing our knowledge of these grades of like- 
ness and unlikeness to a system. By bringing together 
those which are alike, and separating those which are 
unlike, we find that these rest on fixed and inevitable laws. 
Classification is thus defined as " the rational, lawful dis' 
position of observed facts." 

15. Homology. — All rational classification of plants or 
animals concerns itself with homologies. Homology means 
fundamental identity of structure, as distinguished from 
analogy, which means incidental resemblance in form or 
function. Thus the arm of a man is homologous with the 
fore leg of a dog, because in either we can trace throughout 
deep-seated resemblances or homologies with the other. 
In every bone, muscle, vein, or nerve the one corresponds 
closely with the other. The " limb " of a tree, the " arm " 
of a starfish, or the fore leg of a grasshopper shows no such 
correspondence. In a natural classification, or one founded 
on fact, those organisms showing closest homologies are 
placed together. An artificial classification is one based on 
analogies. Such a classification would place together a 

13 



14 



ANIMAL STUDIES 



cricket, a frog, and a kangaroo, because they all jump ; or 
a bird, a bat, and a butterfly, because they all have wings 
and can fly, although, the different kinds of wings are made 
in very unlike fashion. 

16. Natural classification based on homology. — The closest 
homologies are shown by those animals which have sprung 
from a common stock. The basis of natural classification, 
which is an expression of the ancestry of blood relationship 
of animals, is therefore homology. So far as we know, the 
actual presence of homologies among animals implies their 
common descent from some stock possessing the same 
characters. The close resemblance or homology among the 
different races of men indicates that all men originally 

came from one stock. 
As homology implies 
blood-relationship, so, 
on the other hand, 
common descent im- 
plies homology, the 
similar parts being de- 
rived from a common 
ancestral stock. It is 
sometimes said that 
the inside of an animal 
tells what it is, the out- 
side where it has been. 
In the internal struc- 
ture, ancestral traits 
are perpetuated with 
little change through 
long periods. The ex- 
ternal characters, having more to do with surroundings, are 
much more rapidly altered in response to demands of the 
environment. 

A perfect classification would indicate the line of de- 
scent of each member of the series, those now living 




Fig. 2. — Wings showing homology and analogy. 
a, fly ; b, bird ; c, bat. 



PRINCIPLES OF CLASSIFICATION 



15 



having sprung in natural sequence, by slow processes of 
change, from creatures of earlier geological periods. It is 
said that in classification we have " three ancestral docu- 
ments " : Morphology, Embryology, and Paleontology. In 
Morphology we compare one form with another, thus 

a. Elephant. b. Coney. 

'Ill 




Fig. 3. — Homology of digits of four odd-toed mammals, showing gradual reduction 
in number and cousolidation of bones above.— After Komanes. 

tracing resemblances and differences. In Embryology we 
trace the development of individuals from the egg, thus 
finding clues in heredity that will enable us to trace the 
development of the race. In Paleontology we study the 
extinct forms directly, thus often finding evidence as to 
the origin of forms now existing. 

17. Scientific names. — Each of the different kinds of 
animal or plant is called a species. There is no better 
definition of species. Thus the red squirrel is a kind or 
species of squirrel, the gray squirrel is another, the fox 
squirrel a third. The black squirrel of the East is not a 
species, because black squirrels and gray squirrels are some- 
times found in the same nest, born from the same parents. 

A genus is a group of closely related species — one or 
more — separated from other genera by tangible structural 
characters. Thus all the squirrels named above constitute 



±>ftlNCIPLES OF CLASSIFICATION 17 

a single genus. Other squirrel-like animals, as the chip- 
munk, the flying squirrel, the prairie gopher, or the prairie 
dog, belong to as many different genera. 

In the binomial system, invented by Linnaeus and ap- 
plied by him to animals in 1758, the scientific name of an 
animal consists of two words — the name of its genus and 
species taken together. The name of the genus comes 
first. It is a noun, in Latin form, though usually of Greek 
derivation — thus Sciurus, the squirrel, in Greek meaning 
shadow-tail. The name of the species is an adjective in 
meaning, placed after the noun and agreeing with it. 
Thus Sciurus liudsonicus is the name of the red squirrel, 
Sciurus carolinensis of the Eastern gray squirrel, and 
Sciurus ludovicianus of the fox squirrel; Sciuropterus 
volans is the flying squirrel, Tamias striatus the Eastern 
chipmunk, and Sperraopliilus franklini one of the prairie 
gophers. The specific name is usually a descriptive adjec- 
tive — often the name of a locality, sometimes the name of 
a man. The authority usually written after the name of 
an animal is that of the one who gave it its. specific name 
— thus Sciurus liudsonicus Erxleben, which means that 
Erxleben first called it liudsonicus. Usually the name of 
the authority is that of the discoverer of the species. When 
several names are given to the same animal they are called 
synonyms. The earliest of these names is the right name. 
All the rest are wrong. 

18. Families of animals. — A group of related genera is 
called a family. The name of a family is derived from that 
of its principal genus, with the termination idm. Thus all 
the squirrel-like animals belong to the family of Sciuridm. 
All the sorts of mice to the Muridce, from the principal 
genus, Mus, the mouse. The rabbits are LeporidcB, from 
Lepus, the rabbit, and the beavers Castoridce, from Castor, 
the beaver. 

19. Higher groups of animals. — In the higher groups we 
first trace out the different plans of structure. There is 




Fig 5—Three species of jack-rabbits, differing in size, color, and markings but 
believed to be derived from a common stock. The differences have arisen 
through isolation and adaptation. The upper figure shows the head and fore legs 
of the black jack-rabbit (Lepus insularis), of Espiritu Santo Island, Gulf of 
California ; the lower right-hand figure, the Arizona jack-rabbit {Lepus alleni) 
specimen from Port Lowell, Arizona ; and the lower left-hand figure is the San 
Pedro Martir jack-rabbit (Lepus martirensis), from San Pedro Martir Baia 
California. 



PRINCIPLES OF CLASSIFICATION 19 

some question as to the number of these different types, 
but we are not far out of the way in recognizing seven 
principal ones. These give rise to the seven principal 
branches of the animal kingdom : Protozoa, Coslenterata, 
Mollusca, Vermes, Arthropoda, Echinodermata, and Chor- 
data (which includes vertebrates). The followers of Cuvier 
and Agassiz reduced these to four or five : Protozoa, Kadi- 
ata, Mollusca, Articulata, and Vertebrata ; but a more thor- 
ough knowledge of the different groups makes the larger 
number preferable, the radiates and the articulates being 
each divided into two. Many zoologists break up the 
Vermes into several distinct branches. 

The branches are again divided into classes. Thus the 
mammals, birds, reptiles, amphibians, fishes, lampreys, and 
lancelets are classes of vertebrates. The. insects form a 
class of Arthropods. 

Each class is again divided into orders. The Glires or 
rodents, the gnawing animals, of which squirrels, mice, and 
rabbits are examples, form an order of mammals. The 
hoofed animals, Ungulata, form another, and each of these 
again contains many families. 

Intermediate divisions are sometimes recognized, with 
the prefixes super and sub. A subfamily is a division of a 
family including certain genera. A superfamily is a group 
of related families within the limits of an order. 

The red squirrel belongs to the branch Chordata, class 
Mammalia, order Glires, family Sciuridge, genus Sciurus, 
species Hudsonicus. 

20. Trinomial names. — Trinomial names are those in 
which the binomial name of a species is followed by a sec- 
ond adjective. These indicate subspecies or varieties con- 
nected with geographical distribution. Thus many forms 
have a northern variety, a southern variety, one in the 
mountains, one on the plains, in the forests, or in other 
peculiar situations. 

Thus the gray squirrel, typically southern, has a sub- 








*VW_(xavvu Co. 




TPUo/rvvxuO CO 

Fig. 6.— Some chipmunks of California, showing distinct species produced through 
isolation.— From nature, by Willjam Sackston Atkinson. 



PRINCIPLES OF CLASSIFICATION 21 

species, Sciurus carolinensis leucotis (white-eared), in the 
Northern States, larger than the true Sciurus carolinensis, 
with the dark band on the back narrower. In Minnesota 
is another subspecies, Sciurus carolinensis hypophwus, with 
only a narrow streak of white on the belly. As animals 
come to be better known we can recognize by name more 
and more of these subspecies or geographical variations. 

Even in the same locality the members of a species vary 
more or less, no two being exactly alike. The name variety 
is applied to any sort of variation which can be recognized. 
Usually varieties not having definite geographical range re- 
ceive no scientific name. When forms in different geograph- 
ical areas are found to intergrade or mix with one another 
they are known as subspecies, the one first named being re- 
garded as the original species. When they do not intergrade 
they are called distinct species. The subspecies differ from 
the species in degree only. "When the range of a species is 
crossed by an impassable barrier, the subspecies on either 
side of the barrier usually becomes in time a distinct spe- 
cies. Thus distinct species are said to be produced through 
isolation. The plates which follow may serve as illustra- 
tions of species and subspecies thus formed. 



CHAPTER III 

THE SIMPLEST ANIMALS OR PROTOZOA 

21. Single-celled and many-celled animals. — In almost 
every portion of the globe there are multitudes of animals 
whose body consists of but a single cell ; while those forms 
more familiar to us, and usually of comparatively large 
size and higher development, such as sponges, insects, 
fishes, birds, and man himself, are composed of a multitude 
of cells. For this reason the animal kingdom has been 
divided into two great subdivisions, the Protozoa including 
all unicellular forms and the Metazoa embracing those of 
many cells. 

22. Single-celled animals. — The division of the Protozoa 
comprises a host of animals, usually of microscopic size, 
inhabiting fresh or salt water or damp localities on land in 
nearly every portion of the globe. The greater number 
wage their little, though fierce, wars on one another with- 
out attracting much attention ; others, in the sharp struggle, 
have been compelled to live upon or within the bodies of 
other animals, and many have become notorious because of 
the diseases they produce under such circumstances. A 
few are in large measure responsible for the phosphores- 
cence of the sea ; and still others have long been favorite 
objects of study because of their marvelous beauty. Adapted 
for living under diverse conditions, the bodily form differs 
greatly, and yet all conform to three or four principal types, 
of which we may gain a good idea from the study of a few 
representative forms. 

22 



THE SIMPLEST ANIMALS OR PKOTOZOA 



23 



23. The Amoeba. — Among the simplest one-celled ani- 
mals living in the ooze at the bottom of nearly every fresh- 
water stream or pond is the Amosba (Fig. 7, A), whose body 
is barely visible to the nnaided eye. Under the microscope 




Fig. 7.— A, the Amoeba, highly magnified, showing c. v., pulsating vacuole ; /, food 
particle ; n, nucleus. The arrows show the direction of movement. B, shape of 
6ame individual 30 seconds later. C, an amoeba-like animal (Difflugia) partially 
enclosed in a shell. D, an Amoeba in the process of division. E, Gromia, another 
shelled protozoan. — After Schtjlze. 

it is seen to consist of an irregular, jelly-like mass of proto- 
plasm totally destitute of a cell wall. Unlike those animals 
with which we are familiar, the body constantly changes its 
shape. A rounded bud-like projection will be seen to appear 
on one side of the body and the protoplasm of adjacent 
regions flows into it, thereby increasing its extent. Similar 
projections at the opposite end of the cell are withdrawn, 
and their substance may flow into the newly formed lobe, 
which gradually swells in size and pushes forward. Thus, 
by constantly advancing the front part of the body and 



24 ANIMAL STUDIES 

retracting the hinder portion, the cell glides or flows along 
from place to place. 

Upon meeting with any of the smaller organisms upon 
which it lives, projections from the body are put out which 
gradually flow around the prey and it becomes pressed into 
the interior of the cell. The process is not unlike pushing 
a grain of sand into a bit of jelly. There is no mouth. 
Any point on the surface serves for the reception of food. 
Oxygen gas also is taken into the body all over the surface, 
and wastes and indigestible material are cast out at any 
point. Nothing exists in these simple forms comparable to 
the complex systems of organs that carry on these processes 
in the squirrel. 

The bodily size of animals is limited, and to this general 
rule the Amoeba is no exception, for upon gaining a certain 
size, the nucleus divides into two exactly similar portions, 
and very soon afterward the rest of the body separates into 
two independent masses of equal size (Fig. 7, D), each of 
which, when entirely free, contains a nucleus. In this way 
two daughter amoebae are formed possessing exactly the 
characters of the parent save that they are of smaller size ; 
but it is usually not long before they reach their limit of 
growth, when division occurs again, and so on, generation 
after generation. 

It not infrequently happens, however, that the pond or 
stream,* in which the Amoeba and other Protozoa live, dries 
up for a portion of the year. In such an event the body 
assumes a spherical shape, develops a firm, horn-like mem- 
brane about itself, and thus encysted it withstands the sum- 
mer's heat and dryness and may be transported by the wind, 
or otherwise, over great distances. When the conditions 
again become favorable the wall ruptures and the Amoeba 
emerges to repeat its life processes. 

24. Some relatives of the Amoeba. — All amoeba-like forms, 
to the number of perhaps a thousand species, possess this 
same method of locomotion, but many present some inter- 



THE SIMPLEST ANIMALS OR PROTOZOA 25 

esting additional characters. For example, the form repre- 
sented in Fig. 7, C, constructs a sac-like skeleton of tiny- 
pebbles cemented together, into which it may withdraw for 
protection. Others construct similar envelopes of lime or 
flint, and still others, as they continue to grow, build on 
additional chambers, giving rise to a great variety of forms 
often of wonderful beauty. In the tropics, particularly, 
some of the shelled Protozoa are so abundant that they may 
impart a whitish tinge to the water, and in some places 
their empty shells on falling to the bottom form immense 
deposits. The chalk cliffs of England are in large measure 
made up of such shells. 

25. The Infusoria. — A little over two hundred years ago 
it was discovered that wherever water remained stagnant it 
became favorable for the rapid multiplication of a large 
number of species of Protozoa which live in such situations. 
These are known as Infusoria, and, like the preceding spe- 
cies, are usually of microscopic size and of the most varied 
shapes. The first striking feature of their organization is 
the presence of a delicate though relatively firm external 
cell membrane known as the cuticle, which preserves a defi- 
nite shape to the body. Such a method of locomotion as 
exists in the preceding group is consequently an impossi- 
bility, but other and more highly developed structures per- 
form the office. These latter organs are of two types, and 
their general characteristics may be readily understood 
from an examination of a few species living in the same 
localities as the Amoeba. 

26. The Euglena. — The first type exists in the common 
fresh-water organism known as Euglena, represented in 
Fig. 8, A. Here the spindle-shaped body is surrounded by 
a delicate cuticle perforated at one point, where a funnel- 
shaped depression, the gullet, leads into the soft proto- 
plasmic interior. From the base of this depression the 
protoplasm is drawn out in the form of a delicate whip-like 
process known as the flagellum. This structure, always 

3 



26 



ANIMAL STtJDIES 



permanent m form, constantly beats backward and forward 
with great rapidity in a general direction represented in 
the diagram (Fig. 8, c). The movement from a to b is 
much more rapid than the reverse, from b to a, which 
results, like the action of the human arm in swimming, in 
driving the organism forward. Not onl y does the flagel- 
lum serve the purpose of locomotion, but it also produces 
currents in the water which 
may serve to bear minute 
organisms down into the 
gullet, whence they read- 
ily pass into the soft pro- 




Fig. 8. — Flagellate Infusoria. A, 
Euglena viridis ; c, pulsating 
vacuole ; e, eye-spot ; g, gullet ; 
n, nucleus ; t, flagellum. B, Co- 
dosiga, with collar surrounding 
the flagellum. C, diagram illus- 
trating the action of the flagel- 
lum. All figures greatly enlarged. 




Fig. 9. — Parametrium aurelia, a 
ciliate infusorian. c, cilia; c.v., 
pulsating vacuoles ; /, food 
particles ; g, gullet ; m, buccal 
groove ; n, nucleus. 



toplasm of the body, there to undergo the processes of di- 
gestion and assimilation. In some forms the protoplasm in 
the region of the flagellum is drawn out in the form of a 
collar (Fig. 8, B), whose vibratory motion also aids in con- 
veying and guiding food into the body. 

27. The Slipper Animalcule.— The second type of loco- 
motor organ may be understood from a study of the 



THE SIMPLEST ANIMALS OR PROTOZOA 



27 



Slipper Animalcule (Paramecium, Fig. 9), abundant in 
stagnant water. In this form the cuticle surrounding the 
somewhat cylindrical body is perforated by a great number 
of minute openings through which the 
internal protoplasm projects in the form 
of delicate threads. Each process, 
termed a ciliam, works on the same 
principle as the nagellum, but it beats 
with an almost perfect rhythm and in 
unison with its fellows, drives the an- 
imal hither and thither with considera- 
ble rapidity. 

On one side of the body is a furrow 
which deepens as it runs backward and 
finally passes into the gullet (#), which 
leads into the interior of the body. 
Throughout the entire extent it is lined 
with cilia which create strong currents 
in the surrounding water and in this 
way conduct food down the guLet into 
the body. Embedded in the outer sur- 
face of the body, in among the cilia, 
are also a number of very minute sacks, 
each containing a coiled thread which 
may be discharged against the body of 
any intruder, so that this form is sup- 
plied with actual organs of defense. 
Two pulsating vacuoles (c.v.) or simple 
kidneys are also present, consisting of a 
central reservoir into which a number 
of radiating canals extend. 

28. The Bell Animalcule and other 
species. — The Bell Animalcule ( Vorti- 
cella, Eig. 10) is often found in the same situations as the 
Slipper Animalcule, which in certain respects it resembles. 
It is generally attached by a slender stalk, and where many 




Fig. 10.— Vorticetta, an at- 
tached ciliate infusori- 
an. highly magnified, a, 
fully extended individ- 
ual ; c.v., pulsating va- 
cuole ; g, gullet ; n, nu- 
cleus, b, contracted 
specimen, c, small free- 
swimming individual, 
which unites with a sta- 
tionary individual (one 
partly united is shown 
in specimen b). 



28 ANIMAL STUDIES 

are growing together they appear like a delicate growth 
of mold upon the water weed. The stalk is peculiar in 
being traversed by a muscle fiber arranged in a loose spiral, 
which, upon any unusual disturbance, contracts together 
with the body into the form shown in Fig. 10, o. 

These few examples serve to show the general plan of 
organization and the method of locomotion of the Infuso- 
ria ; but, as upward of a thousand species exist, with widely 
differing habits, many interesting modifications are present. 
Some have been driven in past time to adopt a parasitic 
mode of life within the bodies of other animals. At pres- 
ent they are devoid of locomotor organs, and as they absorb 
nutritive fluids through the surface of the body all traces 
of a mouth are also absent. The reproductive processes 
also are peculiar, but they do not concern us now. 

29. Gregarina. — Another type of protozoan worthy of 
special attention is that of the Gregarina (Fig. 11), various 
species of which live in the alimentary canal * of crayfishes 
and centipeds and certain insects. Gregarina is a parasite, 
living at the expense of the host in whose body it lies. It 
has no need to swim about quickly, and hence has no swim- 
ming cilia like Paramecium and the young Yorticella. It 
does need to cling to the inner wall of the alimentary canal 
of its host, and the body of some species is provided with 
hooks for that purpose. The food of Gregarina is the 
liquid food of the host as it exists in the intestine, and 
which is simply absorbed anywhere through the surface of 
the body of the parasite. There is no mouth opening nor 

* Specimens of Gregarina can be abundantly found in the alimen- 
tary canal of meal worms, the larvae of the black beetle (Tenebrio moli- 
tor), common in granaries, mills, and brans. " Snip off with small 
scissors both ends of a larva, seize the protruding (white) intestine with 
forceps, draw it out, and tease a portion in normal salt solution (water 
will do) on a slide. Cover, find with the low power (minute, oblong, 
transparent bodies), and study with any higher objective to suit." — 

MURBACH. 



THE SIMPLEST ANIMALS OR PROTOZOA 



29 



fixed point of ejection of waste material, nor is there any 
contractile vacuole in the body. 

In the method of multiplication or reproduction Gre- 
garina shows an interesting difference from Amoeiba and 
Paramecium and Vorticella, When the Gregarina is 




Fig. 11.— Gregarinidse. A, a Gregarinid {Actinocephalus oUgacanthus) from the in- 
testine of an insect (after Stein) ; B and C, spore forming by a Gregarinid (Coc- 
cidium oviforme) from the liver of a guinea-pig (after Leuckart) ; D, E, and F, 
successive stages in the conjugation and spore forming of Gregarina polymorpha 
(after Koelliker). 

ready to multiply, its body, which in most species is rather 
elongate and flattened, contracts into a ball-shaped mass 
and becomes encysted — that is, becomes inclosed in a tough, 
membranous coat. This may in turn be covered externally 
by a jelly-like substance. The nucleus and the protoplasm 
of the body inside of the coat now divide into many small 
parts called spores, each spore consisting of a bit of the 
cytoplasm inclosing a small part of the original nucleus. 
Later, the tough outer wall of the cyst breaks, and the 
spores fall out, each to grow and develop into a new Gre* 



30 ANIMAL STUDIES 

garina. In some species there are fine dncts or cabals 
leading from the center of the cyst through the wall to the 
outside, and through these canals the spores issue. Some- 
times two Gregarince come together before encystation and 
become inclosed in a common wall, the two thus forming a 
single cyst. This is a kind of conjugation. In some spe- 
cies each of the young or new Gregarince coming from the 
spores immediately divides by fission to form two indi- 
viduals. 

Eelated to the Gregarince are those minute protozoan 
parasites which live in the blood-corpuscles of man and some 
of the lower animals, and are called Hcematozoa. Three 
species of these, living in the blood of man, cause the three 
kinds of malarial fever, known as tertian, quartan, and 
remittent. These malarial Hcematozoa, known generally 
as Hamiamcela, can multiply by asexual sporulation in the 
blood, but produce also certain sexual individuals, which, 
when taken into the stomach of a mosquito which has 
sucked blood from a malarial patient, give rise to a zygote 
which encysts in the outer walls of the stomach, and breaks 
up into numerous blasts or embryos, which escape into the 
blood of the mosquito, and thence to all parts of its body, 
and especially to the salivary or poison glands. When now 
this infected mosquito pierces the skin of another man, 
and pours into the wound, as it regularly does, a quantity 
of saliva, numbers of larval Hcemamcebce also enter the 
blood, and, multiplying here, soon set up the disease 
malaria in the bitten person. It has been definitely proved 
that malaria is thus disseminated by mosquitoes, and it is 
highly probable that it is contracted in no other way. 

30. Characteristics common to the Protozoa. — "We have 
now studied the principal structures which serve in loco- 
motion among these simple one-celled forms, also the means 
by which they catch their food, and we shall now glance at 
the internal processes, which are much the same in all. 

After the food has been taken into the cell, it is proba- 



THE SIMPLEST ANIMALS OR PROTOZOA 31 

bly acted upon by some digestive fluid, for it soon assumes 
a granular appearance, and finally undergoes complete solu- 
tion. In every case the oxygen is absorbed through the 
general surface of the body, and uniting with the living 
substance, as in the squirrel, liberates the energy necessary 
for the performance of the animal's life-work. The wastes 
thus produced in a large number of forms simply filter out 
from the body without the agency of anything comparable 
to a kidney, but in several species they are borne to a 
definite spot, the pulsating vacuole (Figs. 7, 9, 10, c.v.), where 
they gradually accumulate into a drop about the size of the 
nucleus. The wall between it and the exterior now gives 
way, and the excretions are passed out. In active indi- 
viduals this process may be repeated two or three times a 
minute, but it is usually of less frequent occurrence. 

The loss in bodily waste is continually made good by 
the manufacture of the food into protoplasm, and if the in- 
come be greater than the outgo, growth ensues. But, as in 
all other forms, growth is limited, and ultimately the cell is 
destined to divide, resulting in two new individuals. This 
process may be repeated many times, but not indefinitely, 
for sooner or later various members of the same species 
unite in pairs temporarily or permanently, exchange nu- 
clear material, and separate again with apparently renewed 
energy and the ability to divide for many generations. 

31. Simple and complex animals. — It is important to note 
that these same processes of waste, repair, growth, feeling, 
motion, and multiplication are the same as those of the 
squirrel, and, furthermore, are common to all living crea- 
tures, so that the difference between animals is not in their 
activities, but in their bodily mechanisms ; and according 
to the perfection of this, the animal is high or low in the 
scale. Comparing, for example, the Ammba and Slipper 
Animalcule, which are relatively low and high Protozoa, we 
find in the former that any part of the body serves in loco- 
motion and in the capture of food, while in the latter these 



32 ANIMAL STUDIES 

same functions are performed by definite structures, the 
cilia and gullet. Now, it is well known that a workman is 
able to make better watch-springs, when this is his sole 
duty, than another who must make all parts of the watch ; 
and likewise, where a definite task is performed by a defi- 
nite structure, it is more efficiently done than where any 
and every part of the body must carry it on. So the 
Amoeba, in which definite tasks are performed by any part 
of the body indifferently, is less perfect and thus lower than 
the Paramcecium, where these functions are performed by 
special organs. As we ascend the scale of life we find this 
division of labor among special parts of the body more 
complete, the organs, and therefore the animal, more com- 
plex, and better fitted to carry on the work of its life. 



CHAPTER IV 



THE SLIGHTLY COMPLEX ANIMALS OR SPONGES 



32. Their relation to the Protozoa. — While the greater 
number of one-celled forms are not united with their fel- 
lows, there are several species where the reverse is true. In 
Fig. 12, for example, a fresh-water form known as Pandorina 
is represented, consisting of sixteen cells embedded in a 
spherical, jelly-like substance, 
each one of which is precisely 
like its companions in form 
and activity. The aggregation 
may be looked upon as a colo- 
ny of sixteen Protozoa united 
together to derive the benefit 
of increased locomotion and 
a larger amount of food in 
consequence. As a result of 
such a union they have not 
lost their independence, for if 
one be separated from the main 
company it continues to exist. 

From such a simple colonial 
type we may pass through a series of several more complex 
forms which reach their highest development in the beau- 
tiful organism, Volvox (Fig. 13). In this form the indi- 
vidual members, to the number of many thousand, are ar- 
ranged in the shape of a hollow sphere. The united efforts 
of the greater number, which bear on their outer surfaces 
two flagella, drive the colony with the rolling movement 
. 33 




Fig. 12.— Pandorina (from Xature). 
Highly magnified. 



34 



ANIMAL STUDIES 



from place to place. As just indicated, some individuals 
lack the flagella, and their subsequent careers show them 
to be of a peculiar type. Sooner or later each undergoes 

a series of divisions form- 
ing a little globe of ceiis, 
which migrates into the in- 
terior of the parent sphere 
and develops into a new 
colony. Within a short time 
the walls of the parent 
break, liberating the im- 
prisoned young, which con- 
tinue the existence of the 
species while the parent or- 
ganism soon decays. 

Under certain circum- 
stances, instead of develop- 
ing colonies by such a meth- 
od, some of the cells may 
store up food matters and 
become eggs, while others, 
known as sperm-cells, de- 
velop a flagellum, and sep- 
arating from the colony 
swim actively in the sur- 
rounding water, where each 
finally unites with an egg. 
This union, like that of the 
two individuals in Vorticel- 
la (Fig. 10, #, c), results in 
iy the power of division, and 

(from Nature). B, C, and D, reproduc- the efg enters upon its de- 

and again. The cells so pro- 
duced remain together, form a sphere, and finally develop 
a Yolvox colony. 




THE SLIGHTLY COMPLEX ANIMALS OR SPONGES 35 

In such associations as Volvox an important step has 
been taken beyond that of Pandorina, for there is a division 
of the labors of the colony among its various members, 
some acting as locomotor cells while others are germ-cells. 
These are now so dependent one upon the other that they 
are unable to exist after separation from the main com- 
pany, just as a part of the squirrel is incapable of leading 
an independent existence. A higher type of organism has 
thus arisen intermediate between the simple one-celled 
animals and those of many cells, especially the sponges — a 
relation which is more readily recognized after an examina- 
tion of the latter. 

33. Development of the sponge.— Like all many-celled 
animals, the sponge begins its life, however, as a single ceil 
. — the egg — which is in this case barely visible to the sharp 
unaided eye. Fertilized by its union with a sperm cell, 
development commences, and the first apparent indication 
of the process will be the division of the cell into halves 
(Fig. 14, A, B). Each half redivides into four, these again 
into eight cells, and this process is repeated, giving the 
young sponge the general form of Pandorina. The divi- 
sions of the cells still continue and result in the formation 
of a hollow globe of cells (called the blastula, Fig. 14, E, F) 
similar to Volvox, and at this point the young larva leaves 
the parent. 

The next transformation consists in a pushing in of one 
side of the sphere, just as one might press in the side of a 
hollow rubber ball. The depression gradually deepens, and 
finally results in the formation of a two-layered sac known 
as the gastrula (Fig. 14, G). At this stage of its existence 
the sponge settles down for life in some suitable spot, by 
applying the opening of its sac-like body to some foreign 
object. In assuming the final form a new mouth breaks 
through what was once the bottom of the sac, canals per- 
forate the body wall, a skeleton is developed, and the char* 
acteristic features of the adult are thus attained. 



36 



ANIMAL STUDIES 



34. Distribution.— The sponges are aquatic animals, and, 
with the exception of one family consisting of relatively 
few species, all are inhabitants of the sea in every part of 




Fig. 14.— Diagrams illustrating the development of a sponge. A, egg-cell ; n, nucleus. 
B, C, D, 2-, 4-, and 10-cell stages. E, blastula. F, section through somewhat 
older larva. G, gastrula. H, young sponge. I, section through somewhat 
younger larva than H. 

the globe. The larger number occupy positions along the 
shore, becoming especially abundant in the tropics; but 
other species occur at greater depths, several species living 



THE SLIGHTLY COMPLEX ANIMALS OR SPONGES 37 

between three and four miles from the surface. Unlike 
the majority of animals, all members of this group are 
securely fastened to some foreign object, such as rocks, the 
supports of wharves, or with one extremity embedded in 
the sand. As we have seen, the young enjoy a free-swim- 
ming existence and are swept far and wide by means of 
tidal currents, but sooner or later these migrations are 
terminated in some suitable locality, where the sponge 
passes the remainder of its existence. During this time 
some species may never exceed the size of a mustard-seed, 
while others attain a diameter of three feet, or even more. 
Sponges also vary exceedingly in shape, some having the 
form of thin encrusting sheets, others being globular, tubu- 
lar, cuplike, or highly branched (Fig. 15). 

35. The influence of their surroundings. — In by far the 
larger number of cases an animal possesses the bodily form 
of the parent. External agencies may modify this to some 
extent, but usually only to a limited degree. A squirrel, 
for example, resembling its parent, may grow to a relatively 
large or stunted size according to the food supply, and it 
may become strong or weak according to the amount of 
exercise, and various other changes may result owing to 
outside causes ; but as a result of these influences the 
animal is rarely so modified that one is unable to distinguish 
the species. Many of the sponges, however, are exceptions 
to this general rule. If, for example, some of the young 
of a certain parent develop in quiet water or in an un- 
favorable locality, they will usually be low, flat, and un- 
branched ; while the others, growing in swiftly running 
waterways, develop into tall, comparatively delicate and 
highly branched individuals. Under such circumstances 
not only does the external form become modified, but 
the internal organization may undergo profound change. 
The entire organism is plastic and readily molded by 
the influence of its surroundings, and the consequent 
lack of definite characters often renders it impossible 



38 



ANIMAL STUDIES 



to assign such forms to a definite position among the 

sponges. 

36. Structure of a simple sponge. — In the simpler sponges 

the body is usually vase-shaped (Fig. 16), with the base 

fastened to some foreign 
object, while at an oppo- 
site end an opening leads 
into a comparatively large 
internal cavity. This lat- 
ter space is also put in 
communication with the 
exterior by a multitude of 
minute pores which pene- 
trate the body wall. In 




Fig. 15.— Various forms of sponges, natural size. (From Nature.) 

the living condition currents of water continually pass 
through these smaller canals, and out of the large termi- 
nal opening, thus bringing within reach of the body minute 



THE SLIGHTLY COMPLEX ANIMALS OR SPONGES 39 



floating organisms or organic remains which serve as food. 
The mechanism by which this process is effected, and the 
various other structures of the body, are in large part invis' 
ible from the exterior, requiring the 
study of thin sections of the sponge 
to make them clearly understood. 

Under the microscope such a sec- 
tion shows the body of a sponge to 
consist of an immense number of va- 
riously formed cells constituting three 
distinct layers (Fig. 17). Not only 
do these layers consist of different 
kinds of cells, but the duties per- 
formed by each are different. For ex- 
ample, a glance at Fig. 17 will show 
that in the inner layer certain colum- 
nar cells exist, provided with a fla- 
gellum and encircling collar, the ap- 
pearance being strikingly like certain 
of the Protozoa (Fig. 8, B). During 
life their whip-like processes, lashing 
backward and forward in perfect uni- 
son, produce currents of water which 
continually pass through the body. 
The food thus entering the animal is 
taken up by the cells of the inner 
layer as it passes by. The supply, 
however, is usually more than suffi- 
cient to meet the demands of this 
layer, and the excess is passed on to 
the middle and outer layers. The 
exact method by which this occurs is still a matter of 
doubt, but there seems to be little question but that 
each cell of the body receives its food in a practically un- 
modified condition, requiring that it digest as well as 
assimilate. The oxygen necessary to this latter process 




Fig. 16.— One of the sim- 
plest sponges ( Calcolyn- 
thus primigenius (after 
Haeckel). A portion 
of the wall has been re- 
moved to show the in- 
side. 



40 



ANIMAL STUDIES 




is absorbed by all parts of the body in contact with the 

water. 

37. Skeleton of sponges. — When it is remembered that 

the protoplasm composing the cells of the sponge has about 

the same consistence 
as the white of egg, 
it will be readily un- 
derstood why the 
greater number of 
sponges possess a skel- 
eton. Without such 

Fig. 17.— Portion of wall of sponge, showing three a g^-p-port, the larger 

layers, e, outer layer ; i, inner layer, consisting "I to 

of collared cells ; m, middle layer, consisting of globular Or branched 

irregular cells, among which are the radiate spic- forms COllld not ex- 

ules and egg-cells. . n . . 

ist, and even in the 
smaller members there would be danger of a collapse of the 
body walls and consequent stoppage of the food supply, 
owing to the closure of the pores. So in all but a very few 
thin or flat forms a skeleton appears in the young sponge 
almost before growth ....... 

has fairly begun, and ] v^$t#" 
this increases with the 
body in size and com- 
plexity. It is formed 
by the activity of the 
cells of the middle layer, 
and may be composed 
either of a lime com- 
pound resembling mar- 
ble, or of flint, or of a 
horn-like substance resembling silk, or these may exist in 
combination in certain species. When consisting of either 
of the first-named substances it is never formed in one 
continuous piece, but of a vast multitude of variously shaped 
crystal-like bodies termed spicules (Fig. 18). These occur 
everywhere throughout the body, firmly bound together 



Fig. 18.— Different types of sponge spicules. 



THE SLIGHTLY COMPLEX ANIMALS OR SPONGES 41 

by means of cells, or so interlocked that they form a rigid 
support to which the fleshy substance is bound and through 
which the numerous canals penetrate. 

In a relatively few species only does the skeleton con- 
sist of horn, though there are many in which horn and flint 
exist together. In the former event, if the skeleton be 
elastic and of sufficient size, it becomes valuable to others 
than the naturalist, for the familiar sponges of commerce 
are the horny skeletons of forms usually taken in the West 
Indies or in the Mediterranean Sea. In these localities the 
animals are pulled off by divers, or with hooks, and are then 
spread out in shallow water where the protoplasmic sub- 
stance rapidly decays. The remaining skeleton, thoroughly 
washed and dried, is ready for the markets of the civilized 
world. 

Examining a bit of such a " sponge " under a magnify- 
ing glass, it will be seen that the skeleton is not composed 
of various pieces, but of one continuous mass of branching 
fibers, which interlace and unite in apparently the greatest 
confusion ; yet in the living animal these were perfectly 
adapted to the position of the canals and the general needs 
of the animal. 

Besides being a scaffold-work to which the fleshy portions 
of the body are fastened, the skeleton serves also for pro- 
tection. In some species, needle-like spicules as fast as 
they are formed are partly pushed out over the entire sur- 
face of the body, giving the appearance of a spiny cactus ; 
or in other cases they are arranged in tufts about the canals, 
effectually preventing the entrance of any marauder. 
Thus perfectly protected, the sponges have but few natural 
enemies, and hence it is that in favorable localities they 
grow in great profusion. 

38. Race histories and life histories. — We have now traced 
living things from their simplest beginnings, where they 
exist as single cells, and have seen that in bygone times 
similar forms, have united into simple colonies, and these 



42 ANIMAL STUDIES 

through a division of labor among the constituent cells 
have resulted in Volvox-like colonies. There are the strong- 
est reasons for the belief that as these simple forms scat- 
tered into various surroundings and underwent changes to 
meet the shifting conditions, they assumed different de- 
grees of complexity that have resulted in the animal forms 
of the present day. 

It may have been noticed also that the sponge in its 
development passes through these stages : a single-celled 
egg ; later, a young form similar to Pcmdorina, then growing 
to look like Volvox, and finally assuming its permanent form. 
The history of the race of sponges and their development 
through a long line of ancestry of increasing complexity is 
thus told by the sponge as it develops from the egg into 
the adult ; and, so far as we know, all the many-celled ani- 
mals in their growth from the egg repeat more or less 
clearly the stages passed through by their forefathers. 



CHAPTER V 

THE CCELENTERATES 

39. General remarks. — This division of the many-celled 
animals includes the jelly-fishes, sea-anemones, and corals. 
A few species live in fresh water, but the majority are con- 
fined to the sea, being found everywhere from the shore- 
line and ocean surface to the most profound depths. 
Adapted to different surroundings and modes of life, they 
constitute a vast assemblage of the most bewildering di- 
versity. In some cases their resemblance to plants is re- 
markable, and the term zoophyte or " plant animal," occa- 
sionally applied to them, is the relic of former times when 
naturalists confounded them with plants. Even to-day 
certain species are sometimes collected and preserved as 
seaweeds by the uninformed. 

The general plan on which all ccelenterates are con- 
structed is a simple sac, in some respects resembling that 
of the lower sponges, yet, since the modes of life of the 
members of the two groups are usually quite unlike, we 
shall find many profound differences between them. 

40. The fresh-water Hydra.— The bodily plan comes out 
most clearly in the Hydra (Fig. 19, A, D), which occurs 
upon the stems and leaves of submerged fresh-water plants 
in this and other countries. Its body, of a green or grayish 
color, according to the species, scarcely ever attains a diam- 
eter greater than that of an ordinary pin nor a length ex- 
ceeding half an inch. One end of the cylindrical organism 
is attached to some foreign object by means of a sticky 
secretion, but as occasion requires it may free itself, and by 

43 



44 



ANIMAL STUDIES 



means of a " measuring-worm " movement travel to another 
place. 

Examined under a hand lens, the free end of the body 
will be found to support six to eight prolongations known 

as tentacles, vrhich 
serve to convey 
food to the mouth, 
centrally located 
in their midst. 
This opening, un- 
like that of the 
sponges, is the 
only one leading 
directly into the 
large central gas- 
tric cavity which 
occupies nearly 
the entire animal 
(Fig. 19, D). As 
in the sponge, the 
cells of the body 
are arranged in 
the form of defi- 
nite layers, but the 
middle one is rep- 
resented only by 
a thin gelatinous 
sheet. 

41. Organs of 
defense. — These 
are the so-called 
lasso or nettle-cells 
(Fig. 19, C). Some 
of the cells of the outer layer possess, in addition to the 
elements of the typical cell, a relatively large ovoid sac 
filled with a fluid, and also a spirally wound hollow thread 




Fig. 19.— The fresh-water Hydra. A. entire animal, de- 
veloping a new individual (enlarged 25 times). B. C, 
nettle-cells (after Schneider) ; D, section through 
the body. 



THE CCELENTERATES 45 

provided with barbs near its base. On the outer extremity 
of the nettle-cell projects a delicate bristle-like process, the 
trigger hair. These cells are especially abundant on the 
tentacles (Fig. 19, A, D), forming close, knob like eleva- 
tions or "batteries," thus rendering it practically impossible 
for any free-swimming organism to avoid touching them in 
brushing against the tentacles. In such an event the dis- 
turbances conveyed through the trigger hair set up in some 
unknown way very rapid changes in the cell. This causes 
the sac to discharge the coiled thread and barbs into the 
body of the intruder, which is rendered helpless by the par- 
alyzing action of the fluid conveyed through the thread. 
Thus benumbed it is rapidly borne to the mouth and swal- 
lowed. In time new nettle-cells develop to take the place 
of those discharged and consequently worthless. 

42. Digestion of food. — Upon the interior of the body of 
Hydra and all of the ccelenterates the food, by reason of its 
large size, is incapable of being taken into the various cells. 
It is necessary, therefore, to break it up into smaller masses, 
and this is accomplished through the solvent action of the 
digestive fluid poured over it from some of the cells of the 
adjacent inner layer. When subdivided, the granules swept 
about the gastric cavity by the beating of the flagella (Fig. 
19, D) are seized by the processes on the free surfaces of the 
remaining inner layer cells, where they undergo the final 
stages of digestion ; then in a dissolved state they become 
absorbed and assimilated by all the cells of the body. 

43. Methods of multiplication. — Very frequently, espe- 
cially if the Hydra has been well fed, two or three pro- 
cesses arising as outpushings of the body wall may be 
noted upon the sides of the animal (Fig. 19, A, D). If 
these be watched from time to time they are found to in- 
crease in size, and finally, upon their free extremities, to 
develop a mouth and surrounding tentacles. Up to this 
point growth has taken place as a result of the assimilation 
of nutritive substances supplied from the parent ; but a con- 



46 



ANIMAL STUDIES 



ppqr 



T£ 




striction soon occurs which 
separates the young from the 
parent, and from that time 
on the two lead independent 
existences. At other times 
this asexual method of mul- 
tiplication is replaced by sex- 
ual reproduction, where new 
individuals arise from fertil- 
ized eggs. Both eggs and 
sperm arise in Hydra and in 
some other animals in the 
same individual, but in all 
such cases the eggs are fertil- 
ized by sperm which escape 
from some other individual. 
The fertilized egg, surround- 
ed by a firm coat, separates 
from the parent, drops to the 
bottom, and after a period of 
rest develops into a little Hy- 
dra which hatches and enters 
upon a free existence. 



Fig. 20.— Different types of Hydrozoan 
colonies. From Nature, the lower 
species magnified about 50 diameters. 




THE CCELENTERATES 47 

44. Hydrozoa, or Hydra-like animals.— Attention has al- 
ready been directed to the fact that the structure of Hydra 
is the simplest of the ccelenterates ; nevertheless, the thou- 
sand or more species belonging to this class which present 
a much more complicated appearance (Fig. 20) possess 
many fundamental Hydra-like characters. It is owing to 
this fact that this assemblage of forms has been placed in 
the class of the Hydrozoa, or Hydra-like animals. 

With but very few exceptions the members of this class 
are marine, usually living near the shore-line, where at 
times their plant-like bodies occur in the greatest profusion 
attached to rocks, seaweeds, or the bodies of other animals, 
particularly snails and crabs. Fig. 20 (upper colony) gives 
a good idea of one of the more complex forms, whose tree- 
like body attains in some cases the relatively giant height of 
from 15 to 25 cm. (six to ten inches). In early life it bears 
a close resemblance to a Hydra. Buds form in much the 
same way, but they retain permanently their connection with 
the parent, and in turn bear other buds, until finally the form 
shown in the figure is attained. In the meantime root-like 
processes have been forming which afford firm attachment 
to the object upon which the body rests. Also during this 
process the cells of the outer layer form a horny external 
skeleton ensheathing the entire organism except the ter- 
minal portions (the hydranths, Fig. 21, B) bearing the ten- 
tacles. The gastric cavities of all communicate, and the 
food captured by one ministers in part to its own needs 
and, swept through the tubular stalks and roots, is also 
shared by all other members. 

45. Jelly-fishes and the part they play. — During the pro- 
cess of growth a number of stubby branches arise which 
differ from the ordinary type in shape, and also in many 
cases as regards color. These club-like, fleshy portions de- 
velop close-set buds (Fig. 21, c) which early assume a bell- 
like shape, the point of attachment corresponding to the 
handle, while the clapper is represented by a short, slender 



48 



ANIMAL STUDIES 



process bearing on its end an opening which becomes the 
mouth (Fig. 21, A). Around the margin of the bell nu- 
merous tentacles develop, and at the same time the gelati- 
nous substance situated between the outer and inner layers 
of the bell expands to a relatively enormous degree, giving 
it an increasing globular form and glassy appearance. 




Fig. 21.— A jelly-fish (Gonionemus), slightly enlarged. The stalked mouth is shown 
in dotted outline. B, C, enlarged portions of a hydroid colony bearing the 
mouth and tentacles ; j, a capsule within which the jelly-fish develop ; D, dia- 
gram of jelly-fish, illustrating its method of locomotion. 

Finally, vigorous movements rupture the connection with 
the parent, and this newly developed outgrowth, usually 
small, becomes an independent organism popularly termed 
a jelly-fish. While the external form of the jelly-fish appears 
to be widely different from the hydranths, a more careful 
study shows the difference to be superficial. Some zoolo- 
gists believe that jelly-fishes are simply buds which have 
become fitted to separate and swim away from the colony 
in order to distribute the young, as described hereafter. 
When the stalked colonies are very abundant the jelly- 



THE CCELENTERATES 49 

fishes may be liberated in such multitudes that the upper 
surface of the ocean for many miles may be closely packed 
with them in numbers reaching far into the millions. In 
these positions they are carried both by oceanic currents 
and through the alternate expansion and contraction of the 
bell, a movement resembling the partial closing and open- 
ing of an umbrella. In the jelly-fish the contraction is 
more vigorous and rapid than the opening in the velum or 
veil (Fig. 21, b) which is so narrowed that the water in 
the subumbrella space (a) is driven through it with con- 
siderable force, which results in driving the body in the 
opposite direction. 

The life of a jelly-fish is perhaps of short duration, last- 
ing not more than a few hours in some species, up to two 
or three weeks in others, but during that period they pro- 
duce multitudes of eggs which develop into minute free- 
swimming young. These settle down on some rock or sea- 
weed, and soon develop a Hydra-like body which, after the 
fashion described above, grows into another tree-like colony. 

46. Alternation of generations. — It will be noticed that 
the offspring of the jelly-fishes are not jelly-fishes, but stalked 
colonies, and these latter forms give rise to jelly-fishes. 
This is known as the alternation of generations, the jelly- 
fish generation alternating with the colonial form. This 
characteristic is of the greatest service in preventing the 
extermination of the race. Were the stalked forms to 
give rise directly to other stationary colonies, it is obvious 
that before long all the available space in the immediate 
locality would be filled. The food supply, always lim- 
ited, would not suffice, and starvation of some or imper- 
fect development of all would result ; but by means of the 
free-swimming jelly-fish new colonies are established over 
very extensive areas, and favorable situations are held 
by all. 

47. More complex types. — As mentioned above, there are 
perhaps upward of a thousand species of Hydrozoa, all with 



50 



ANIMAL STUDIES 



essentially the same structure but with various modes of 
branching (for some of the commoner modes, see Fig. 20). 
In some of the higher forms a division of labor has arisen 
among various members of the association which has led to 
most interesting results. For example, Fig. 22 represents 
a species of hydroid found investing the shells of sea-snails 
occupied by hermit crabs (Fig. 66). To the unaided eye 
its appearance is that of a delicate vegetable growth, but 
when placed under the microscope it is found to consist of 

a multitude of Hydra-like 
animals united by a hollow 
branching root system con- 
necting the gastric cavities 
of all of them (Fig. 22). 
Certain individuals (a) 
with tentacles and a mouth 
resemble a Hydra ; others, 
without a mouth and ten- 
tacles, are reduced to a 
club-like form (b) liberally 
supplied with nettle-cells 
upon their free extremi- 
ties; while the third type 
(c), likewise devoid of a mouth, possesses rudiments of ten- 
tacles below which are borne numerous clumps of repro- 
ductive cells. The first type, the only one possessing a 
mouth, captures the food, and after digesting it distributes 
the greater portion to the remaining members by means of 
the connecting root system ; those of the second form, de- 
fending the others by means of their nettle-cells against 
the inroads of a foreign enemy, are the soldiers of the colo- 
ny; while the third type produces the eggs from which 
new individuals develop. 

In some of the higher Hydrozoa, the Portuguese man- 
of-war (Fig. 23), this division of labor has reached a more 
advanced stage of development, and in addition the entire 




Fio. 22.— An enlarged portion of a hydroid 
colony {Ilydraclinia), showing (a) the 
nutritive polyp, {b) the defensive polyp, 
and (c) the reproductive polyp. 



THE CCELENTERATES 



51 



colony is fitted for a free-swimming existence. What cor- 
responds ordinarily to the attached stalk in other forms 
terminates in a bladder-like expansion, distended with 
gas, that serves as a float. From it are suspended individ- 
uals resembling great stream- 
ers sometimes many feet in 
length, without mouths, but 
loaded with nettle-cells that 
enable them to capture the 
food, which is conveyed to the 
second type, the nutritive 
polyps. Each of these is a 
simple tube bearing a mouth, 
and within them the food is 
digested and distributed by 
means of a branching gastric 
cavity extending throughout 
the entire colony. Then there 
are individuals like mouthless 
jelly-fishes which bear the 
eggs and care for the perpet- 
uation of the colony ; and be- 
sides these there may be some 
whose duty it is to defend the 
rest, and others whose active 
swimming movements, to- 
gether with the wind, drive 
the colony about. Thus uni- 
ted, sharing the food supply 
and working for the general welfare of all, the members of 
this colony live in greater security and with less effort than 
if, as separate individuals, each was fighting the battles of 
life alone. 

48. Scyphozoa. — The greater number of the larger and 
more conspicuous jelly-fishes are included under this term. 
In general shape and locomotion they resemble those of the 




A colonial jelly-fish (Physalia). 
From Nature. 



52 



ANIMAL STUDIES 



preceding group (Fig. 24), but while the latter are generally 
very small, these forms are commonly from four to twelve 
inches in diameter, and some measure one to two meters 
(three to six feet) across the bell. They are also distin- 
guished by means of tentacles which extend from the cor- 
ners of the mouth sometimes to a distance of several feet, 

and together with the 
marginal tentacles are 
formidable weapons for 
capturing small crabs, 
fishes, and other ani- 
mals which serve as 
food. In turn these 
forms serve as the food ' 
of many whales, por- 
poises, and numerous 
fishes which hunt them 
down, though the 
amount of nourishment 
they contain is prob- 
ably relatively small 
owing to the fact that 
in their composition 
there is a large percent- 
age of water (99 per 
cent in some species). The lobed margin of the bell, the 
absence of a definite swimming organ or velum, and the 
character of several of the internal organs, distinguish the 
larger from the smaller jelly-fish ; but the greatest differ- 
ence, however, is in the method of development. 

49. Development. — The eggs arise from the inner layer 
of the jelly-fish and drop into the gastric cavity, where each 
develops into a ciliated two-layered sac in some respects 
like that of a young sponge. Swimming away from the 
parent, they finally settle down, and attaching themselves 
(Fig. 25, a) assume the external form and habits of the sea- 




Fig. 24.— A jelly-fish (Rhizos(oma), about one- 
fourth natural size. 



THE CCELENTERATES 



53 



anemones, described in the next section. In the course of 
time remarkable changes ensue, which first manifest them- 




Fig. 25.— Stages in the development of a scyphozoan jelly-fish, a, the attached 
young, which in b has separated into a number of disks, each of which becomes a 
jelly-fish, c— After Korschelt and Heider. 

selves in a series of grooves encircling the body. These 
grow deeper, and the body of the animal finally comes to 
resemble a pile of sau- 
cers with the edge of 
each developed into a 
number of lobes (Fig. 
25, b). One after an- 
other each saucer, to 
preserve the simile, 
raises itself from the 
top of the pile and 
swims away, and is 
clearly seen to be a 
jelly-fish, though con- 
siderably unlike the 
adult. As growth pro- 
ceeds, however, it un- 
dergoes a series of transformations which result in the 
adult form- 




Fig. 26.— An attached scyphozoan jelly-fish 
{Halidystus). Natural size, from Nature. 



54 



ANIMAL STUDIES 



50. Sea-anemones. — In its external appearance the sea- 
anemone (Fig. 27) bears some resemblance to the Hydra, bnt 
is of a mnch larger size (1 to 45 cm., or \ inch to \\ feet 
in diameter), and is frequently brilliantly colored. The 
number of tentacles is also more numerous, and the mouth 
leads into the body by means of a slender esophagus (Fig. 
28). Numerous partitions from the body wall extend in- 
ward, and many unite to the esophagus, keeping the latter 




Fig. 27.— Sea anemones (the two upper figures) and solitary coral polyps. 



in position. Below the esophagus each partition projects 
into the great cavity of the body and bears upon its inner 
free edge several important structures. The first of these, 
known as the mesenteric filaments (Fig. 28), appearing like 
delicate frills, plays an active part in the digestion of the 
food. Associated with these are long, slender threads, 



THE CCELEXTERATES 



55 



closely packed with innumerable lasso-cells, which may be 
thrown out through openings in the body wall when the 
animal is attacked. Lasso-cells are also very numerous on 
the tentacles, which are thus to some extent defensive, but 
are chiefly active in capturing the crabs and small fish 
which serve as food. 

The partitions also carry eggs which may undergo the 
first stages of their growth within the body, and when 
finally able to swim 
are sent out through 
the mouth opening 
by hundreds to seek 
out favorable situa- 
tions, there to set- 
tle down and re- 
main. In some spe- 
cies the young may 
sometimes arise as 
buds, as in Hydra 
(Fig. 27), and in 
others the animals 
have been described 
as splitting longi- 
tudinally into two 
equal -sized young. 

51. Corals.— The 
coral polyps also 

belong to this group, 1 showing a very close resemblance to 
the sea-anemones. In most cases they develop a firm skel- 
eton of lime, commonly known as " coral," which serves to 
protect and support the body. In a few species the polyps 
throughout life are solitary, and with skeleton comparative- 
ly simple (Fig. 27) ; but the larger number of species be- 
come more complex by developing "feuds, which retain their 
connection with the parent, and in turn produce other out- 
growths with the ultimate result that highly branched 




Fig. 28.— Longitudinal section through the body of a 
sea-anemone, oe, esophagus ; m. /., mesenterial 
filaments ; r., reproductive organs. 



56 ANIMAL STUDIES 

colonies are produced (Fig. 29). At the same time the 
outer layer of the body is continually forming a skeleton 
which encloses the colony as a sheath, except at the ter- 
mination of each branch, where the mouth and tentacles 
are located. In certain species — for example, the sea pens 
(Pennatula) and sea fans (Gorgonia) — a skeleton may be 




1 portions of coral colonies, with some of the potyps expanded. 



formed of myriads of lime spicules, somewhat like those 
of the sponge, which are bound together by the fleshy 
substance of the body ; but the skeleton of most of the 
common forms in the ocean, and the coral found in 
general collections, is stony. According to their method 
of branching, such specimens have received various popu- 
lar names, such as brain, stag-horn, organ-pipe, and fun- 
gous corals. 




Fig. 30.— Coral island (Nanuku Levu, of the Fiji group). (After a photograph 
hy Max Agassiz.) 




Fig. 31.— Shore of a coral island, with cocoanut palms. (After a photograph.) 
5 



58 ANIMAL STUDIES 

Nearly all species, like the sea-anemones, are brilliantly 
colored during life, and several are highly phosphorescent. 
All are marine, and while they are found everywhere, from 
the shore-line to great depths, the more abundant and 
larger species inhabit the clear, warm waters of the tropics 
down to a depth of one hundred and sixty feet. In such 
regions the stag-horn corals especially grow in the wildest 
profusion, and become tall and greatly branched. Except 
in quiet water they are continually being broken by the 
waves, beaten into fragments, and the resulting sand is 
deposited about their bases. As a result of this continu- 
ous growth and erosion, there have been formed from coral 
sand mixed with the shells of mollusks and the skeletons 
of various Protozoa several of the islands along the Florida 
coast and many of those of the Pacific, some of them 
hundreds of miles in extent. 



CHAPTER VI 

THE WORMS 

52. General Characteristics. — The bodies of the animals 
comprising the two preceding groups are exposed on all 
sides equally to the water in which they live and are radi- 
ally symmetrical ; but in the worms, one side of the body 
is fitted for creeping, and for the first time we note a well- 
marked dorsal (back) and ventral (under) surface. In the 
former, the body, like a cylinder, may be divided into simi- 
lar halves by any number of planes passing lengthwise 
through the middle ; but in the worms, the right and left 
halves only are exposed equally to their surroundings, and 
there is, accordingly, only one plane which divides the body 
into corresponding halves, so that these animals, like all 
higher forms, are bilaterally symmetrical. In creeping, also, 
one end of the body is directed forward and it thus be- 
comes correspondingly modified. It usually bears the 
mouth, and may be provided with eyes, feelers, or organs 
of touch, and various other structures which enable the 
worm to recognize the nature of its surroundings. The 
nervous and muscular systems are better developed than in 
the foregoing groups, and we note a greater vigor and defi- 
niteness in the animal's movements, and in various ways the 
worms appear better able to avoid or ward off their enemies, 
recognize and select their food, and in general adapt them- 
selves to the conditions of life. 

The division of the worms is a very large one, and in 
some respects difficult to define, owing to the close resem- 

59 



60 



ANIMAL STUDIES 



blance which many of them show to animals in other 
groups. All the invertebrates, therefore, except the crabs 
and insects, were placed in one group until subsequent 
study made it possible to classify them more exactly. Ac- 
cording to the general shape of the body, and the arrange- 
ment of internal organs, worms are divided into a number 
of groups, chief among which are the fiatworms, the thread 
or roundworms, and the ringed worms or annelids. 

The Flatwoiois 

53. Form and habitat. — The fiatworms, as their name 
indicates, are much flattened, leaf-like forms, some species 
living in damp places on land, 
in fresh - water streams or 
ponds, or along the seacoast, 
while a variety of other spe- 
cies are parasitic. The free 
forms (Fig. 32) are usually 
small, barely reaching a length 
greater than five or seven cen- 
timeters (2 to 3 inches), but 
some of the parasitic species 
(Fig. 36) attain the great 
length of six to thirteen me- 
ters (20 to 40 feet). 

The free-living forms usu- 
ally occur on the under side 
of stones, and frequently are 
so delicate that a touch is 
sufficient to destroy them. A 

few Species are almost trans- Fig. 32.-A, fresh-water flatworm (Ha- 
. . ., , naria); B, marine flatworm t Lepto- 

parent, While many are COl- plana) _ Enlarged, from Nature. 

ored to harmonize completely 

with their surroundings, so that, even though fragile and 
defenseless, they escape the attacks of enemies by being 
overlooked. The night-time or dark days are their hunting 




THE WORMS 



61 



season, and at such periods they may be found moving about 
with a steady gliding motion (due to cilia covering the en- 
tire body), varied occasionally by a looping, caterpillar move- 
ment, or by swimming with a napping of the sides of the 
body. When watched at such times they may sometimes 
be seen to snatch up small worms, snails, small crabs and 
insects, which serve as food. 

More closely examining one of these forms, for example, 
the species usually found on the under side of sticks and 
stones in our shallow fresh-water streams (Fig. 32, A), we note 
that the forward end is not developed into a well-defined 

head as in the higher worms, 
but is readily determined by 
the presence of very simple 
eyes and tentacles, while the 
lower creeping surface is dis- 
tinguished by a lighter color 
and the presence of the 
mouth. Through this small 
opening a slender proboscis 
(in reality the pharynx) may 
be extended some distance, 
and may be seen to hold the 
small organisms upon which 
it lives until they are suffi- 
ciently digested to be taken 
into the body. 

54. Digestive system.— In 
the smaller flatworms, some 
of which are scarcely larger 
than many of the Protozoa, 
the alimentary canal is a sim- 
ple unbranched tube ; but in 
the larger forms such an ap- 
paratus is replaced by a greatly branched digestive tract 
which furnishes an extensive surface for the rapid absorp- 




-Anatomy of fresh-water flat- 
worm (Planaria). exs, escretory sys- 
tem, with flame-cell (/). The ali- 
mentary canal is stippled. B, nerv- 
ous system. 



G2 



ANIMAL STUDIES 



tion of food, and extending deep into the tissues of the 
body, carries nutriment to otherwise isolated regions. In 
the fresh-water forms and their allies there are three main 
branches of the intestine (Fig. 33), while in many of those 
from the sea there are several, and their arrangement 
affords a basis for their general classification. 

55. Excretory system. — In the sponges and ccelenterates 
the wastes are cast out by the various cells into the gastric 
cavity or at once to the exterior with- 
out the aid of any pronounced system 
of vessels; but in the flatworms sev- 
eral of the organs are deeply buried 
within the tissues of the body and a 
drainage system becomes a necessity. 
This consists of a paired system of ves- 
sels extending the length of the ani- 
mal (Fig. 33) and provided with numer- 
ous branches, some of which open at 
various points on the surface of the 
body, while the others terminate in 
spaces (Fig. 34, s) among the organs in 
what are known as flame-cells. The 
substances which accumulate in these 
spaces are gathered up by the flame- 
cell, poured into the space it contains, and by means of the 
vibratory motion of its flagellum (/), a movement bearing 
a fancied resemblance to the flickering of a flame in the 
wind, are borne through the tubes to the exterior. 

56. Nervous system and sense-organs. — In the sponges no 
definite nervous system is known to exist, the slight move- 
ments which the cells are able to undergo being regulated 
somewhat as they are in the Protozoa. Among the ccelen- 
terates certain of the cells scattered over the surface of the 
body are set aside as nerve-cells, and, more or less united by 
means of fibers extending from them, convey impulses over 
the body. In the flatworms the larger number of nerve-cells 




Fig. 34.— Flame-cell of flat- 
worm (after Lang). /, 
flagellum ; n, nucleus; 
8, spaces among the or- 
gans of the body ; v, 
waste materials. 



THE WORMS 63 

are collected into two definite masses (Fig. 33, B), which 
constitute a simple brain on which the eyes are situated 
and from which bundles of nerve fibers pass to all parts of 
the body, the two extending backward being especially 
noticeable. As in the squirrel, these are distributed to the 
muscles and other organs to regulate their activity, while 
those distributed to the skin, especially in the forward 
part of the body, convey stimuli produced by touch. The 
branches connecting with the eyes enable the animal to 
distinguish light from darkness, but are probably too sim- 
ple to allow it to clearly distinguish objects of the outside 
world. The sense of smell and possibly that of taste are 
also present, but are relatively feeble. 

Some other characters of this class will be noted in the 
consideration of the two following classes. 

57. Parasitic flatworms (trematodes) — parasitism. — Men- 
tion has already been made of the associations of two ani- 
mals as "messmates" for mutual benefit, such as the Hy- 
dractinia growing on the surface of the shell inhabited by 
the hermit crab, to which it gives protection by means of 
its nettle-cells, while in turn being borne continually into 
regions abounding with food. More frequently, however, 
one animal derives benefit from another without making 
any compensation. For example, many species of flatworms 
live within the shells of certain snails and upon the bodies 
of sea-urchins and starfishes, where they gather in their 
food supply safe from the attacks of enemies. Such asso- 
ciations are probably without much if any inconvenience to 
the animal thus inhabited, and it also appears probable 
that the tenants are transients, using the mollusk or star- 
fish only as a temporary home. But from this condition of 
affairs it is only a short step to the parasitic habit, where 
the association becomes permanent and the occupant is 
provided with various structures which prevent its sepa- 
ration from its host. This latter kind of union occurs 
throughout the group of trematodes ; all are parasitic, and 



64 



ANIMAL STUDIES 



their internal organization, so closely resembling that of 
the free-living forms as to need no further description, in- 
dicates that they are 
descendants of the lat- 
ter. In the greater 
number the body is 
flat, and a few species 
still retain their outer 
coat of cilia ; but since 
these are no longer of 
service as locomotor 
organs they have gen- 
erally disappeared, and 
in their place numer- 
ous adhesive organs, 
such as spines, hooks, 
and suckers (Fig. 35), 
have arisen, which en- 
able the animals to 
hold on with great te- 
nacity. Thus attached 
to its host, and using 
it as a convenient and 
comparatively safe 
means of locomotion, 
the parasite may still 

continue to capture, small animals for food or may derive 
its nourishment from the tissues of the host. In addition 
there are numbers of internal parasites, living almost ex- 
clusively in the bodies of vertebrate animals, scarcely a sin- 
gle one escaping their ravages. 

58. Life history. — In the external parasites the young 
hatch out and with comparative ease make their way to 
another host ; but the young of an internal parasite, inhab- 
iting the alimentary canal, have a very slight chance in- 
deed of ever reaching a similar location in another host. 




Fig. 35. — A parasitic flatworm (Epidella). m 
mouth ; o, opening of reproductive system ; 
s, sucker and spines for attachment. The di- 
gestive system is stippled ; nervous system 
black. Enlarged 8 times, from Nature. 



THE WORMS 65 

For this reason an almost incredible number of eggs is laid, 
and some extraordinary measures are employed in effecting 
the desired result. Probably the best-known example is that 
of the liver fluke inhabiting the bile-ducts in the sheep. 
Each worm lays several hundred thousand eggs, which make 
their way from the host, and if they chance to fall in pools 
of water or damp situations may proceed to develop, other- 
wise not. If the surroundings be favorable, the young, like 
little ciliated Infusoria, escape from their shells and rest- 
lessly swim or move about for a short time, and if during 
this time they come in contact with certain species of 
snails living in these situations they at once bore into their 
bodies. Here they produce other young somewhat resem- 
bling a tadpole, that now make their escape from the snail. 
In a short time each one crawls upon a blade of grass, and 
surrounds itself with a tough shell, where it may remain for 
several weeks. If the grass on which they rest be eaten by 
a sheep, they finally make their way to the bile-ducts and 
there become adult. The life cycle is now complete ; the 
young form has found a new host ; and the process shows 
how wonderfully animals are adapted to the conditions which 
surround them, and how closely they must conform to these 
conditions in order to exist. 

59. The tapeworms (cestodes). — The cestodes, or tape- 
worms, are also parasitic flatworms in which the effects of 
such a mode of life are strongly marked. They occur 
almost exclusively in the bodies of vertebrate hosts and 
exhibit a great variety of bodily forms, in some cases resem- 
bling rather closely the trematodes, but in others strikingly 
different. In the latter type the body is usually of great 
length (from a few centimeters to upwards of sixteen meters 
(50 feet) ), and terminates in a "head" (Fig. 36) provided, 
in the different species, with a great variety of hooks and 
spines and numbers of suckers for its attachment to the 
body of the host. From the head the body extends back- 
ward in the gradually enlarging ribbon-like body, slender at 



66 



ANIMAL STUDIES 




first and scarcely showing the segments which finally be- 
come so prominent a feature. 

When carefully examined, a two-lobed brain is found 
in the '" head," and from it nerves extend the entire length 
of the body, followed throughout their 
course by the tubes of the excretory 
system ; also each segment contains a 
perfect reproductive system, so that 
even if it be separated from the others 
it may continue to exist for a consid- 
erable length of time. Furthermore, 
the tapeworms are surrounded by the 
predigested fluids of their host; a 
special alimentary canal is therefore 
superfluous, and all traces of it have 
disappeared. 

60. Development. — As the animal 
clings in this passive way to the body 
of its host the segments, loaded with 
eggs ready for development, separate 
one after another from the free end 
of the body, pass to the exterior, and 
slowly crawling about like independent organisms, lay great 
numbers of eggs, which may find an intermediate host as in 
the life cycle of the liver fluke, and so in time find their 
permanent resting-place. Fortunately in all these parasitic 
forms, though an inconceivably great number of eggs are 
laid, only a comparatively few reach maturity. Even these, 
however, may cause at times great destruction among the 
higher, and especially our domestic, animals, often doing 
damage amounting to many millions of dollars per year. 

61. The tapeworm in relation to regeneration.— It has 
been known for more than one hundred and fifty years that 
some of the lower animals possess to a surprising degree 
the ability to regenerate parts of the body lost through 
injury. The Hydra, hydroids, and some of the jelly-fishes 



g. 36.— Tapeworm (Tcenia 
solium). In upper left- 
hand corner of figure is 
the much enlarged head. 
—After Leuckart. 



THE WORMS 67 

may be cut into a number of pieces, each of which will 
develop into a complete individual ; and this power of recov- 
ery from the injuries produced by enemies is of the great- 
est service in the perpetuation of the species. This ability 
is also present in certain flatworms, and some species are 
known which voluntarily separate the body into two por- 
tions, each of which becomes an adult. In other species a 
similar process results in the formation of a chain of six 
individuals, placed end to end, the chain finally breaking 
up into as many complete worms. It is possible that the 
tapeworm may also be looked upon as a great chain of 
united individuals produced by the division of a single 
original parent, which becomes adapted for attaching the 
others until they separate. These latter are capable only of 
a very sluggish movement, and, devoid of mouth and ali- 
mentary canal, are not able to digest their food, but their 
life work is to so lay their eggs that they may develop into 
other individuals, and for this they are well adapted. 

Nematodes (Threadworms) 

62. General characters.— This class of worms is com- 
posed of an enormous number of different species, some para- 
sitic, others free all or a portion of their lives, and in view of 
the fact that they inhabit the most diverse situations it is 
remarkable that they are so uniform in their structure. In 
all the body is slender, and the general features of its organ- 
ization may be readily understood from an examination of 
the "vinegar eel" (Fig. 37, A). This small worm (not an 
eel), a millimeter or two in length, lives on the various forms 
of mold that grow in fermenting fruit juices, especially 
after a little sugar or paste has been added. A tough cuti- 
cle surrounds the body, preserving its shape and at the 
same time protecting the delicate organs against the action 
of the acids in which it lives. Through this may be seen 
great bands of muscles extending the entire length of the 
body and producing the wriggling movements of swimming 



68 



ANIMAL STUDIES 




or crawling. They also give support to a brain, which is 
in the form of a collar encircling the pharynx near the 
head, and to the great nerves which extend from it. Still 
further within the transparent body the alimentary canal 
may be distinguished as a straight 
tube passing directly through the 
animal. The alimentary canal lies 
freely in a great space, the body 
cavity, traces of which may exist 
in the flatworms in the form of 
hollow spaces into which the kid- 
neys open. It is possible that in 
this form also the kidneys open 
into this space, and it is roomy 
enough besides to afford lodgment 
for the reproductive organs in 
addition to a large amount of fluid 
which is probably somewhat of 
the nature of blood. A space in 
some respects similar to this occurs 
in all the animals above this group, 
and as we shall see, it is often cu- 
riously modified and serves for a 
number of different and highly im- 
portant purposes. • In the round- 
worms the fluid it contains proba- 
bly acts in the nature of a blood 
system, distributing the food and 
oxygen to various parts of the body and carrying the wastes 
to the kidneys for removal. 

63. Multiplication. — In the matter of the production of 
new individuals the greatest differences exist. In some 
threadworms, for example the " vinegar eel," eggs develop 
within the body and the young are born with the form of the 
parent. In other cases the eggs are laid in the water, where 
they, too, may directly grow to the adult condition ; but in 



Fig. 37. — Thread- or round 
worms. A, vinegar eel (An- 
guillula) ; m, mouth ; ph. 
pharynx ; i, intestine ; ov. 
developing young. B. Tri- 
china. From Nature, greatly 
enlarged. 



THE WORMS 69 

the greater number of species the development is round- 
about, and one or more hosts are inhabited before the young 
assume the adult condition. Such is the case with the 
dreaded Trichina (Fig. 37, B), which infests the bodies of 
several animals, particularly the rat. When these forms 
are introduced into the alimentary canal of the rat, for 
example, they soon lay a vast quantity of eggs, sometimes 
many millions, which develop into young that bore their 
way into the muscles of the body, where they may remain 
coiled up for years. If the body of the rat be eaten by some 
carnivorous animal, these excessively small young are lib- 
erated during the process of digestion and rapidly assume 
the adult condition in the alimentary canal, likewise giving 
rise to young which pursue again the same course of de- 
velopment. 

Another example of a complicated life history is in 
the Gordius or " horsehair snake " (a true worm and not a 
snake) frequently seen in the spring in pools where it lays 
its eggs. These eggs develop into young which bore their 
way into different insect larvae, which are in turn eaten by 
some spicier or beetle, and the worm thus transferred to a 
new host. In this they grow to a considerable size, and 
then make their exit from the body of the host and finally 
become adult. 

64. Spontaneous generation. —The ancients believed that 
many animals were spontaneously generated. The early 
naturalists thought that flies arose by spontaneous genera- 
tion from the decaying matter of dead animals ; from a 
dead horse come myriads of maggots which change into 
flesh flies. Frogs and many insects were thought to be 
generated spontaneously from mud. Eels were thought to 
arise from the slime rubbed from the skin of fishes. Aris- 
totle, the Greek philosopher, who was the greatest of the 
ancient naturalists, expresses these beliefs in his books. It 
was not until the middle of the seventeenth century — 
Aristotle lived three hundred and fifty years before the 



70 ANIMAL STUDIES 

birth of Christ — that these beliefs were attacked and be- 
gan to be given np. William Harvey, an English natural- 
ist, declared that every animal comes from an egg, but that 
the egg might "proceed from parents or arise spontane- 
ously or out of putrefaction." In the middle of the same 
century Eedi proved that the maggots in decaying meat 
which produce the flesh flies develop from eggs laid on the 
meat by flies of the same kind. Other zoologists of this 
time were active in investigating the origin of new indi- 
viduals. And all their discoveries tended to weaken the 
belief in the theory of spontaneous generation. 

Finally the adherents of this theory were forced to 
restrict their belief in spontaneous generation to the case 
of parasites and the animalcules of stagnant water. It was 
maintained that parasites arose spontaneously from the 
matter of the living animal in which they lay. Many para- 
sites have so complicated and extraordinary a life history 
that it was only after long and careful study that the truth 
regarding their origin was discovered. No case of spon- 
taneous generation among parasites is known. If some 
water in which there are apparently no living organisms, 
however minute, be allowed to stand for a few days, it will 
come to be swarming with microscopic plants and animals. 
Any organic liquid, exposed for a short time, becomes 
foul through the presence of innumerable bacteria, etc. 
But it has been certainly proved that these organisms are 
not spontaneously produced by the water or organic liquid. 
A few of them enter the water from the air, in which there 
are always greater or less numbers of spores of microscopic 
organisms. These spores germinate quickly and the rapid 
succession of generations soon gives rise to the hosts of 
bacteria and Protozoa which infest all standing water. 
If all the active organisms and inactive spores in a glass 
of water are killed by boiling the water, " sterilizing " it, 
as it is called, and this, sterilized water be put into a 
sterilized glass, and this glass be so well closed that germs 



THE WORMS 



71 



or spores can not pass from the air without into the steril- 
ized liquid, no living animals will ever appear in it. It is 
now known that flesh will not decay or liquids ferment 
except through the presence of living animals or plants. 




•The multiplication of Amoeba by simple fission. 



To sum up, we may say that we know of no instance of the 
spontaneous generation of organisms, and that all the ani- 
mals whose life history we know are produced from other 
animals of the same kind. " Omne vivum ex vivo" All life 
from life. 



72 ANIMAL STUDIES 



Annelids or Segmented Worms 

65. The earthworms and their relatives. — Leaving the 
groups of the parasitic animals, which have been driven from 
the field of active existence and in many ways are degraded 
by such a mode of life, we pass on to the higher free-living 
worms, where brilliant colors, peculiar habits, or remarkable 
adaptations render them peculiarly interesting. In consid- 
ering first their general organization, we may use the earth- 
C 



W 

Fig. 39.— Earthworm (Lumbricus terrestris). m, mouth ; c, girdle or clitellum. 

worm (Fig. 39) (sometimes called angle-worm or fish-worm) 
as a type because of its almost universal distribution. 

The body is cylindrical, shows well-marked dorsal and 
ventral surfaces, and, as in all of the annelids, is jointed, 
each joint being known as a segment. Anteriorly it tapers 
to a point, and the head region bearing the mouth is ill- 
defined, unlike many sea forms, yet serves admirably for 
tunneling the soil in which all earthworms live. In this 
process the animal is also aided by bristles or setce which 
project from the body wall of almost every segment and 
may be stuck into the earth to afford a foothold. 

06. Food and digestive system. — The earthworms are 
nocturnal animals, seldom coming to the surface during the 
day except when forced to do so by the filling of their tun- 
nels with water or when pursued by enemies. At night 
they usually emerge partially, keeping the posterior end of 
the body within the burrow, and thus they scour the sur- 
rounding areas for food, which they appear, in some cases 
at least, to locate by a feeble sense of smell. They also 
frequently extend their habitations, and in so doing swallow 
enormous quantities of earth from which they digest out 
any nutritive substances, leaving the indigestible matter in 



THE WORMS 73 

coiled " castings " at the entrance of the burrows. In thus 
mixing the soil and rendering it porous they are of great 
service to the agriculturist. 

Although earthworms are omnivorous they also manifest 
a preference for certain kinds of food, notably cabbage, 
celery, and meat, which leads us to think that they have a 
sense of taste. All these substances are carried into their 
retreats and devoured, or are used to block the entrance 
during the day. The food thus carried into the body is 
digested by a system (Fig. 40) composed of several portions, 




rw 

1c. K s / 6 6d. \d 

Fig. 40. — Earthworm (Lumbricus) dissected from left side, b, brain ; c, crop ; d, 
outer opening of male reproductive system ; dv, dorsal blood-vessel ; g, gizzard ; 
h, pulsating vessels or " hearts " ; i, intestine ; k, kidney ; m, mouth ; n. c, nerve- 
cord ; oe, esophagus ; o, ovary ; od, oviduct ; ph, pharynx ; r, testes ; s.r., sem- 
inal receptacles ; v. v., ventral vessel. 

each of which is modified for a particular part in the pro- 
cess. The mouth (m) leads into a muscular pharynx (ph) 
whose action enables the worm to retain its hold on various 
objects until swallowed, and this in turn is continuous with 
the esophagus. From here the food is passed into the thin- 
walled crop (c),and from this storehouse is gradually borne 
into the gizzard (g), whose muscular walls reduce it to a fine 
pulp now readily acted upon by the digestive fluids. These, 
resembling in their action the pancreatic juice of higher 
animals, are poured out from the walls of the intestine into 
which the food now makes its way ; and as it courses down 
this relatively simple tube the nutritive substances are ab- 
sorbed while the indigestible matters are cast away. 

67. Circulatory system. — In all the groups of animals up 
to this point the digested food is carried through the body 
by a simple process of absorption, or in the threadworms by 



74 



ANIMAL STUDIES 



means of the fluid in the body cavity ; but in the earthworm 
the division of labor between different parts of the body is 
more perfect, and a definite blood system now acts as a 
distributing apparatus. This consists primarily of a dorsal 
vessel lying along the dorsal surface of the alimentary canal 
(Fig. 40), from which numerous branches are given off to 
the body wall, and to the digestive system through which 
they ramify in every direction before again being collected 
into a ventral vessel lying below the digestive tract. In 
some of the anterior segments a few of the connecting 
vessels are muscular and unbranched, and during life pul- 
sate like so many hearts to force the blood over the body, 
forward in the dorsal vessel, through the " hearts " into the 
ventral vessel, thence into the dorsal by 
means of the small connecting branches. 

Some of the duties of this vascular 
system are also shared by the fluid of 
the body cavity, which is made to cir- 
culate through openings in the parti- 
tions by the contractions of the body 
wall of the animal in the act of crawl- 
ing. In this rough fashion a consider- 
able amount of nutritive material and 
oxygen are distributed to various or- 
gans, and wastes are carried to the kid- 
neys to be removed. 

68. Excretion. — In nearly all of the 
segmented worms there is a pair of 
kidneys to every segment (Figs. 40, 41). 
Each consists of a coiled tube wrapped in a mass of small 
blood-vessels, and at its inner end communicating with the 
body cavity by means of a funnel-shaped opening. In 
some unknown way the walls of the kidney extract the 
waste materials from the blood-vessels coursing over it and 
pass them into its tubular cavity. At the same time the 
cilia about the mouth of the funnel-shaped extremity are 




Fig. 41.— Diagram of earth- 
worm kidney, b, blood- 
vessel ; /. funnel open- 
ing into body cavity ; 
o. outer opening ; s, 
septum ; to, body wall. 



THE WORMS 75 

driving a current from the body-cavity fluids, which wash 
the wastes to the exterior. 

69. Nervous system. — The nervous system of the earth- 
worm consists first of a brain composed of two pear-shaped 
masses united together above the pharynx (one shown in 
Fig. 34), from which nerves pass out to the upper lip and 
the head, which are thus rendered highly sensitive. Two 
other nerves also pass out from the brain, and, coursing 
down on each side of the pharynx like a collar, unite below 
it and extend side by side along the under surface of the 
digestive system throughout its entire extent. In each 
segment the two halves of this ventral nerve-cord are united 
by a nerve, and others are distributed to various organs, 
which are thus made to act and in proper amount for the 
good of the body as a whole. 

In its relation to the outside world the chief source of 
information comes to the earthworm through the sense of 
touch, for definite organs of sight, taste, and smell are but 
feebly developed, while ears appear to be entirely absent. 
Nevertheless these are sufficient to enable it to lead a suc- 
cessful life, as is evidenced by the great number of such 
worms found on every hand. 

70. Egg-laying. — In digging up the soil where earth- 
worms abound one frequently finds small yellowish or 
brownish bodies looking something like a grain of wheat. 
These are the cocoons in which the earthworms lay their 
eggs, and the method by which this is performed is unique. 
We have already noted the presence of a swollen girdle 
(the clitellum) about the body of the worm. At the breed- 
ing season this throws out a fluid which soon hardens into 
an encircling band. By vigorous contractions of the body 
this horn-like collar is now slipped forward, and as it passes 
the openings of the reproductive organs the eggs and 
sperms are pushed within it. They thus occupy the space 
between the worm and the collar, and when the latter is 
shoved off over the head its ends close as though drawn to- 



7ti 



ANIMAL STUDIES 



gether by elastic bands. A sac, the cocoon, is thus pro- 
duced, containing the eggs and a milky, nutritive substance. 
In a few weeks the worm 
develops and, bursting the 
wall of its prison, makes its 
escape. 

71. Distribution. — The 
earthworms and their allies 
are found widely distributed 
throughout the world, and 
all exhibit many of the 
characters just described. 
The greatest differences 
arise in their mode of life : 
some are truly earthworms, 
but others are fitted for a 
purely aquatic existence in 
fresh water or along the 
geacoast ; a few have taken 
up abodes in various ani- 
mals and plants, and in 
some of these situations they 
extend far up the sides of 
the higher mountains. In 
all, the head is relatively 
indistinct, the number of 

bristles On each Segment Fig. 42. -A marine worm (Nereis). A ap- 

few, and for this and other 
reasons all are included in 
the subclass Oligochaeta, or " few-bristle " worms. 

72. Nereis and its allies.— In many of the above-men- 
tioned situations members of a more extensive group of 
worms are found, with highly developed heads and many 
bristles arranged along the sides of the body. These are 
the Polychsetes or " many-bristle " worms, and as a repre- 
sentative we may take Nereis (Fig. 42), a very common 




pearance at breeding season, and B, 
at other times. 



THE WORMS 



77 



form along almost any seashore. The body presents the 
same segmented appearance as the earthworm, but the 
head (Fig. 43, A) is provided with numerous sense organs, 
chief among which are four eyes and 
several tentacles or "feelers.'"' 

The segments behind the head 




Fig. 43. — A, head and one of the lateral appendages CB) of a marine worm (Xereis 
brandtii) ; al, intestine ; /, " gill " ; k, kidney ; n, nerve cord ; s, bristles for loco- 
motion. 

differ very little from one another, and, unlike those of 
the earthworm, each bears a pair of lateral plates (Figs. 
41, 42, B) or paddles with many lobes, some of which bear 
numerous bristles. By a to-and-fro movement these organs 
aid in pushing the animal about, or may enable certain spe- 
cies to swim with considerable rapidity. 

As in all other worms, respiration takes place through 
the surface of the body, the area of which is increased by 
the development, on certain portions of the paddles (para- 
podia), of plates penetrated with numerous blood-vessels, 
which thus become special respiratory organs or gills 
(Fig. 42, B). 

In their internal organization the Polychsetes are con- 
structed practically on the same plan as the earthworms, 
the principal difference being in the reproductive system. 
In the earthworm this is restricted to some of the forward 
segments, while in the present group the eggs and sperms 



78 



ANIMAL STUDIES 



are developed in almost every segment, whence they are 
finally swept to the exterior through the tubes of the kid- 
neys (Fig. 43, B). 

The Nereis and its immediate relatives are all active 
forms, and by means of powerful jaws, which may be quickly 
extended from the lower part of the mouth cavity, they 
capture large numbers of small crustaceans, mollusks, and 
worms which happen in their path. Others more distantly 
related make their diet of seaweed, and 
many living on the sea bottom swallow 
great quantities of sand, from which they 
absorb the nutritious substances. 

73. Sedentary forms. — Preyed upon by 
many enemies, a large number of species 
have been forced to abandon an active ex- 
istence save in their early youth, and to 
construct many interesting devices for their 
protection. Numerous species, shortly after 
they commence to shift for themselves? 
build about their bodies tubes of lime (Fig. 
45), from which they may emerge to gather 
food and into which they may dash in times 
of danger. As the worm grows the tube is 
correspondingly enlarged, and these tubes, 
in all stages of construction and variously 
coiled, may be found on almost every avail- 
able spot at the seashore, and may often 
be seen on the shells of oysters in the 
markets. 

In other species the tube is like thin 
horn, and may be further strengthened or 
concealed by numerous pebbles, bits of carefully selected 
seaweeds, or highly tinted shells, which give them a very 
attractive appearance. Such species usually develop out 
of immediate contact with other forms, but a few live 
so closely associated together that their twisted tubes 




Fig. 44.— A common 
marine worm kPo- 
lyna. brevisetosa), 
with extended pro- 
boscis and over- 
lapping plates cov- 
ering the back. 



THE WORMS 



79 



form great stony masses, sometimes several feet in diam- 
eter. 

74. Effects of an inactive life. — In many species such a 
sedentary life has resulted in the almost complete disap- 
pearance of the lateral appendages, which therefore no 
longer serve as organs of respiration, and this function has 
been shifted accordingly on to other structures. These 
new organs are situated principally on the exposed head, 




Fig. 45.— Sedentary tube-dwelling marine worms, upper left hand Sabella (.one-nalf 
natural size), the remainder Serpula (enlarged twice). From life. 

and Fig. 39 shows the general appearance of some com- 
mon species. The corners of the mouth have expanded 
into great plumes, sometimes wondrously colored like a 
full-blown flower, and these, bounteously supplied with 
blood-vessels, act as gills. When disturbed, the plumes are 
hastily withdrawn into the tube, and some of the so-called 
serpulids (Fig. 45, bottom of figure) close the entrance with 
a funnel-shaped stopper. While the plumes are primarily 
respiratory organs, they also act as delicate feelers, and may 
even bear a score or more of eyes ; and in addition, being 



80 



ANIMAL STUDIES 



covered with cilia, create the currents of water which 
bring minute organisms serving as food within reach of 
the mouth. 

75. Development. — Unlike the earthworms, the Poly- 
chsetes lay their eggs in the sea water, where they are left 
alone to develop as best they may. Both the male and 
female Nereis, as the egg-laying time approaches, undergo 
remarkable changes in their external appearance, resulting 
in the form shown in Fig. 42, A. 
They are now active swimmers, and 
thus are able to scatter the fertilized 
eggs over wide and more or less favor- 
able areas. The young also for a 
time are free-swimming, but finally 
end their migrations by settling to 
the sea bottom, where they gradually 
attain the adult condition. 

As in some of the flatworms, re- 
production may also occur asexually 
by the division of the animal into two 
or more parts, each of which subse- 
quently becomes a complete indi- 
vidual. In other species growth of 
various parts may result in two com- 
plete worms at the time of separation ; 
and from such forms we may trace a 
fairly complete series up to those in 
which the original parent breaks up Fi6.46.-Aieech(jfaeroW* 

, , . , la). Right-hand figure il- 

intO twenty to thirty young. lustrates alimentary canal. 

76. The leeches. — At first Sight P*- pharynx ; c, crop ; p, 

the leeches (Fig. 46), or at least the 
smaller, more leaf-like forms, might 
be mistaken for flatworms, especially for some of the para- 
sitic species. As in the latter, the mouth is surrounded by 
a sucker, and another is located at the hinder end of the 
body, but beyond this point the resemblance ceases. The 




lateral pouches ; 
testine. 



THE WORMS 81 

outer surface is delicately marked off into eighty or a hun- 
dred rings, of which from three to five are included in one 
of the deeper true segments corresponding to those of 
other annelids. From two to ten pairs of simple eyes are 
borne on the head, and owing to the fact that they are 
active swimmers, or move by caterpillar-like looping, loco- 
motor spines are unnecessary and absent. In their internal 
organization, however, there are many features which in- 
dicate a close relationship with the Oligochgetes or few- 
bristle worms. The nervous, circulatory, and certain char- 
acteristics of the excretory systems are decidedly similar, 
but, on the other hand, there are some facts difficult to 
explain, which have led some zoologists to believe that 
the relationship of these animals can not at present be 
determined. 

77. Haunts and habits. — The leeches usually dwell in 
among the plants in slowly running streams, but some 
occur in moist haunts on land, and a considerable number 
live in the sea. All are " bloodsuckers " — fierce carnivo- 
rous worms, whose bite is so insidiously made that the vic- 
tim frequently is ignorant of their presence. Fishes, frogs, 
and turtles are the most frequently attacked, but cattle and 
other animals which come down to drink also become their 
prey. In some of the tropical countries the land-leeches 
are present in large numbers secreted among the leaves, and 
so severe are their attacks that various animals, even man, 
succumb to their united efforts. Adhering by their suck- 
ers, they puncture the skin, some using triple jaws, and 
fill themselves until they become greatly distended, when 
they usually drop off and digest the meal at leisure. In 
certain species the intestine is provided with lateral 
pouches (Fig. 45), which serve to store up the food until 
the time for digestion arrives. A full meal is sufficient 
with some species to last for two or three months, and the 
medicinal or horse-leech when gorged with food may con- 
sume a year in digesting it. 



82 ANIMAL STUDIES 

78. Egg-laying. — The eggs of some leeches are stored 
up in a cocoon like that of the earthworm, which is attached 
to submerged plants or placed under stones. When the 
young are able to lead independent lives they emerge with 
the form of the parent. A leaf -like form, Clepsine, some- 
times found adhering to turtles, fastens the eggs to the 
under side of its body, and the young when hatched 
remain there for several days, adhering by their posterior 
suckers. 



CHAPTER VII 

ANIMALS OP UNCERTAIN RELATIONSHIPS 



In this chapter we shall consider in a brief way a number 
of different groups of animals whose relationships are un- 
certain. Up to the present time the study of their habits, 
structure, and development has been of too fragmentary 
or unrelated a character to enable the majority of zoologists 
to agree upon their classification. .Nevertheless, many of 
them are highly interesting and attractive, 
often very common, and in some respects 
they hold important positions in the animal 
kingdom. 

79. The rotifers or wheel-animalcules. — 
The rotifers or wheel-animalcules are rela- 
tively small and beautiful organisms, rarely 
ever longer than a third of an inch, but at 
times so abundant that they may impart a 
reddish tinge to the water of the streams 
and ponds in which they live. At first 
sight they might be mistaken for one-celled 
animals, but the presence of a digestive 
tract and of reproductive elements soon dis- 
pels such a belief. Examined under the 
microscope, the more common forms are 
seen to possess an elongated body terminat- 
ing at the forward end in two disk-like expansions beset 
along the edges with powerful cilia. These serve to drive 
the animal about, or, when it remains temporarily attached 

83 




Fig. 47.— A wheel- 
animalcule {Rotifer). 



84 ANIMAL STUDIES 

by the sticky secretion of the foot, to sweep the food-par- 
ticles down into the mouth. Through the walls of the 
transparent body such substances are seen to pass into the 
stomach, where they are rapidly hammered or rasped into 
a pulp by the action of several teeth located there. In 
the absence of a circulatory system the absorbed food is 
conveyed by the fluid of the body-cavity, which also con- 
veys the wastes to the delicate kidneys. Several other 
features of their organization are of much interest, espe- 
cially to the zoologist, who believes that he gains from 
their simple structure some ideas of the ancestors of the 
modern worms, mollusks, and their allies. During the 
summer the rotifers lay two sizes of "summer eggs," 
which are remarkable for developing without fertilization. 
The large size give rise to females, the smaller to males, the 
latter appearing when the conditions commence to be un- 
favorable. The " winter eggs," fertilized by the males and 
covered with a firm shell, are able for prolonged periods to 
withstand freezing, drought, or transportation by the wind. 
The adults also are able under the same adverse conditions 
to surround themselves with a firm protective membrane 
and to exist for at least a year. Once again in the presence 
of moisture the shell dissolves, and in a surprisingly short 
space of time they emerge, apparently none the worse for 
the prolonged period of quiescence. 

80. Gephyrea. — There is a comparatively large group of 
worm-like organisms, over one hundred species in all, which 
at present hold a rather unsettled position in the animal 
kingdom. Some of the more common forms (Fig. 48) 
living in the cracks of rocks or buried in the sand, usually 
in shallow tide pools along the seashore, have a spindle- 
shaped body terminated at one end by a circlet of tentacles 
which surround the mouth. On account of their external 
resemblance to many of the sea-cucumbers (Fig. 95), they 
were earlier associated in the same group ; but an examina- 
tion of their internal organization inclines many zoologists 



ANIMALS OF UNCERTAIN RELATIONSHIPS 85 

to the belief that the ancestors of some of these animals 
were segmented worms whose present condition has arisen 
possibly in accordance with their sluggish habits. This 
view is strengthened by the fact that in a very few species 

the larvae are dis- 
tinctly segmented, 
but lose this char- 
acter in becoming 
adult. As before 
mentioned, the 
J£ / | greater number of 

species live in bur- 
rows in the sand 
or crevices in the 
rocks, from which 
^^HMMsSSS \ Hfc\ they reach out and 

gather in large 
quantities of sand. 
As these substances 

Fig .48.— A gephyrean worm (Dendrostoma). Specimen pass down the in- 
on left opened to show k, kidney, m, muscle bands, , ,. , n , • 

and n.c, nerve-cord. testme the nutri " 

tive matters are di- 
gested and absorbed, while the indigestible matters are 
voided to the exterior. When large numbers are associated 
together they are doubtless important agents in modifying 
the character of the sea bottom, thus acting like the earth- 
worms and their relatives. 

81. The sea-mats (Polyzoa). — The sea-mats or Polyzoa 
constitute a very extensive group of animals common on 
the rocks and plants along the seashore, and frequently 
seen in similar situations in fresh-water streams. A few 
lead lives as solitary individuals, but in the greater number 
of species the original single animal branches many times, 
giving rise to extensive colonies. In some species these 
extend as low encrusting sheets over the objects on which 
they rest; while in others the branches extend into the 




80 



ANIMAL STUDIES 



surrounding medium and assume feathery shapes (Fig. 49), 
which often bear so close a resemblance to certain plants 




Fig. 49.— Lamp-shells or Brachiopods (on left of figure), fossil and living, and (on 
right) plant-like colonies of sea-mats. 

that they are frequently preserved as such. What their 
exact position is in the animal scale it is somewhat difficult 
to say ; but judging especially from their development, it 
appears probable that they are distant relatives of the seg- 
mented worms. 



ANIMALS OF UNCERTAIN RELATIONSHIPS 87 

82. Lamp-shells or Brachiopods.— Occasionally one may 
find cast on the beach or entangled in the fishermen's 
lines or nets a curious bivalve animal similar to the form 
shown in Fig. 49. These are the Brachiopods, or lamp- 
shells. The remains of closely related forms are often 
abundant as fossils in the rocks (Fig. 49). Over a thousand 
species have been preserved in this way, and we know that 
in ages past they flourished in almost incredible numbers 
and were scattered widely over the earth. Unable to adapt 
themselves to changing conditions or unable to cope with 
their enemies, they have gradually become extinct, until 
to-day scarcely more than one hundred species are known. 
These are often of local distribution, and many are com- 
paratively rare. 

For a long period the Brachiopods, owing to their pecul- 
iar shells, were classed together with the clams and other 
bivalve mollusks. The presence of a mantle also strength- 
ened the belief; but closer examination during more recent 
years has shown that the shells are dorsal and ventral, and 
not arranged against the sides of the animal as in the 
clams. Another peculiar structure consists of two great 
spirally coiled " arms," which are comparable in a general 
way to greatly expanded lips. The cilia on these create, in 
the water currents which sweep into the mouth, the small 
animals and plants that serve as food. The internal organ- 
ization resembles in a broad way that of the animals con- 
sidered in the previous section, and it now appears that 
both trace their ancestry back to the early segmented 
worms. 

83. Band or nemertean worms. — In a few cases band or 
nemertean worms have been discovered in damp soil or in 
fresh-water streams. These are commonly small and incon- 
spicuous, and are pigmies when compared with their marine 
relatives, which sometimes reach a length of from fifty to 
eighty feet. Many of the marine species (Fig. 50) are often 
found on the seashore under rocks that have been exposed 



88 



ANIMAL STUDIES 



by the retreating tide. They are usually highly colored 
with yellow, green, violet, or various shades of red, and are 
so twisted into tangled 
masses that the differ- 
ent parts of the body 
are indistinguishable. 
As the animal crawls 
about, a long thread- 
like appendage, the pro- 
boscis, is frequently shot 
out from its sheath at 
the forward end of the 
body and appears to be 
used as a blind man 

nsPQl-nq stink At otllPr Fig. 50.-A band or nemertean worm. A, entire 

uses nis suck. At otner worm . B headj bearing numerous eye8 and 

times, when Small WOrmS spine-tipped proboscis. 

and other animals are 

encountered, the proboscis is shot out farther and with 
greater force, impaling the victim on a sharp terminal spine 
(Fig. 50). The food is now borne to the mouth, located 
near the base of the proboscis, is passed into the digestive 
tract, traversing the entire length of the body, and is far- 
ther operated on by systems of organs too complex to be 
considered here. 




CHAPTER VIII 

MOLLUSKS 

84. General characters. — For very many years the mol- 
lusks — that is, the clams, snails, cuttlefishes, and their allies 
— have been favorite objects of study largely because of the 
durability, grace, and coloration of the shell. The latter 
may be univalve, consisting of one piece, as in the snails, or 
bivalve, as in the clams and mussels, and may possess almost 
every conceivable shape, and vary in size from a grain of 
rice to those of the giant clam (Tridacna) of the East Indian 
seas, which sometimes weighs five hundred jDounds. These 
external differences are but the expression of many internal 
modifications, which, while adapting these animals for dif- 
ferent modes of life, are yet not sufficient to disguise a 
more fundamental resemblance which exists throughout 
the group. In some respects the mollusks show a close 
resemblance to the annelid worms, but, on the other hand, 
the body is usually more thick-set and totally devoid of any 
signs of segmentation. In every case the skin is soft and 
slimy, demanding moist haunts and usually the protection 
of a shell, and the body is modified along one surface to 
form a foot or creeping disk which serves in locomotion. 
The internal organization is somewhat uniform, and will 
admit of a general description later on. Mollusks are 
divided into three classes, viz. : The Lamellibranchs, em- 
bracing the clams ; the Gasteropods, or snails ; and the 
Cephalopods, or cuttlefishes, squids, and related forms. 

85. Lamellibranchs (clams and mussels). — Numerous rep- 
resentatives of this class, such as the clams and mussels, 

7 89 



90 ANIMAL STUDIES 

occur along our seacoasts or are plentifully distributed in 
the fresh-water streams and lakes. They are distinguished 
from other mollusks by a greatly compressed body, which 
is enclosed in a shell consisting of two pieces or valves 
locked together by a hinge along the dorsal surface. Rais- 
ing one of these valves, the main part of the body may be 
seen to occupy almost completely the upper (dorsal) part 
of the shell (Fig. 51), and to be continued below into the 
muscular hatchet-shaped foot (ft.), which aids the clam in 
plowing its way through the sand or mud in which it lives. 
Arising on each side of the back of the animal and extend- 
ing its entire length is a great fold of skin, which com- 
pletely lines the inner surface of the corresponding valve 
of the shell. These are the two mantle lobes (m) instru- 
mental in the formation of the shell, and enclosing between 
them a space containing the foot and a number of other 
important structures, the most conspicuous of which are 
the gills (g), consisting of two broad, thin plates attached 
along the sides of the animal and hanging freely into the 
space (mantle cavity) between the mantle and the foot. 
Owing to this lamella-like character of the branchia or gills 
the class derives its. name, lamellibranch. To illustrate the 
relations of these various organs to one another the clam has 
been compared to a book, in which the shells are repre- 
sented by the cover, the fly-leaves by the mantle lobes, the 
first two and last two pages by the gills, and the remaining 
leaves by the foot. In the clams, however, the halves of 
the mantle, like the halves of the shell, are curved, and 
thus enclose a space, the mantle cavity, which is partly 
filled by the gills and foot. 

Unlike the other mollusks which usually lead active 
and more aggressive lives, the clams show scarcely a sign of 
a head and tentacles, and other sense organs are likewise 
absent from this region. The mouth also lacks definite 
organs of mastication, and as devices for catching and 
holding food are not developed, the food is brought to the 



MOLLUSKS 



91 



mouth by means of the cilia on the great triangular lips or 
palps which bound it on each side (Fig. 51, A,p). 

Ji i • 




Fig. 51.— Anatomy of fresh-water clam. A, right valve of shell removed ; B, dissec- 
tion to show internal organs, a, external opening of kidney ; a.a., the anterior 
muscle for closing the shell ; 5, opening of reproductive kidney ; c, brain ; ft., 
foot ; g, gill ; h, heart ; i, intestine ; k, kidney ; I, liver ; m, mantle (upper fig.), 
mouth (lower fig.) ; p. palp (upper fig.), foot nerves (lower fig.) ; p.a., hinder 
muscle for closing the shell ; s, space through which the water passes on 
leaving the body ; st, stomach ; v, nerves supplying viscera. 

Between the halves of the shell in the hinge region is a 
horny pad that acts like a spring, and without any muscu- 
lar effort on the part of the clam keeps the shells open. 



92 ANIMAL STUDIES 

These are also united by two great adductor muscles, located 
at opposite ends of the animal (Fig. 51, A, a.a.,p.a.), which 
in times of disturbance contract and firmly close the shell. 
Upon their relaxation the shell opens, the clam extends its 
foot, and plows its way leisurely through the mud, or re- 
mains buried, leaving only the hinder portion of its gaping 
shell exposed. Through this opening a current of water 
is continually passing in and out, owing to the a-otion of 
the cilia covering the gills, and by placing a little car- 
mine or coloring matter in the ingoing stream we may 
trace its course through the body. Passing in between the 
mantle and the foot it travels on toward the head, giving 
off small side streams which are continually made to enter 
minute openings in the gills, whence they are conducted 
through tubes in each gill up to a large canal at its base, 
where it is carried backward to the exterior. In this pro- 
cess oxygen gas is supplied to the number of blood-ves- 
sels traversing the gills, and at the same time considerable 
quantities of minute organisms and organic debris are 
hurried forward toward the head, where they encounter the 
whirlpools made by the cilia on the lips and are rapidly 
whisked down into the mouth and swallowed. 

86. Rock- and wood-boring clams. — Other similar forms 
are rendered even more secure through their ability to 
bore in solid rock. In the common Piddock, for example 
(Fig. 52), the shell is beset with teeth like a rasp, which 
gradually enlarge the cavity as the animal grows, until it 
becomes a prisoner with no means of communication with 
the exterior save the small opening through which the 
siphons project. This is also the case with the Teredo, 
frequently called the shipworm, which swims about for 
some time during early life and then, about the size of a 
small pinhead, settles down upon the timbers of wharves 
or unsheathed ships, into which it rapidly tunnels. 
Throughout life its excavation is extended sometimes to a 
distance of two to three feet, and imprisoned yet safe at 



MOLLUSKS 



93 



the bottom of its burrow, it extends its slender siphons up 
the tube and out of the entrance for its food supply. 
Often hundreds of individuals enter the same piece of 
wood, which becomes thoroughly riddled within a short 




Fig. 52.— The piddock (Zirphcea crispata), a rock-boring niollu 
from life. 



time, and though giving no outward sign of weakness may 
collapse with its own weight. Incalculable damage is thus 
rendered to the shipping interests, and in consequence 
much has been done to check their ravages, but they are 
fai from being completely overcome. 

87. Other stationary species. — A large number of other 
species, while small and inconspicuous, are also free to 



94 



ANIMAL STUDIES 



move about, but as they become larger they lose this ability 
either wholly or periodically. In the edible mussels (Myti- 
lus, Fig. 53), for example, which are associated in great 
numbers on the rocks along our coasts, the foot early be- 
comes long and slender and capable of reaching out a con- 
siderable distance from the shell to attach threads (byssus), 
which it spins, to foreign objects. These are remarkably 
strong, and when several have been spun it becomes a mat- 
ter of much difficulty to dislodge them. After remaining 
anchored in one situation for a while the mussel may vof- 




Pig. 53.-The edible mussel (Mytilus edulis), showing the threads by which it is 
attached. Natural size, from life. 

untarily free itself, and in a labored fashion move to some 
other more favorable spot where it again becomes attached, 
but there are numerous species, such as "fan shells" 
(Pinna), scallops, Anomia, and a few fresh-water forms, 
where the union is permanent. 

Finally, in the oysters, some of the scallops, and a num- 
ber of less familiar forms, the young in very early life drop 
down upon some foreign object to which the shell soon 
becomes firmly attached, and in this same spot they pass 
the remainder of their lives. The oyster usually falls upon 
the left half of its shell, which becomes deep, and capacious 
enough to contain the body, while the smaller right valve 



MOLLUSKS 95 

acts as a lid. As locomotion is out of the question, the foot 
never develops,, and the shell is held by only one adductor 
muscle, whose point of attachment in the oyster is indicated 
by a brown scar in the interior of the shell. 

88. Internal organization.— It is thus seen that the ex- 
ternal features of the clam are variously modified, according 
to the life of the animal, but the internal organization is 
much more uniform. In nearly every species the food con- 
sists of floating organisms, which are driven by the palps 
into the mouth and on to the simple stomach, where it is 
subjected to the solvent action of the fluids from the liver 
(Fig. 51, B, I) before entering the intestine. This latter 
structure is usually of considerable length, and in the active 
species extends down into the foot, and it is also peculiar in 
passing through the ventricle of the heart. Traversing the 
intestine the nutritive portion of the food is absorbed, and is 
conveyed over the body by a circulatory system more highly 
developed than in the higher worms. On the dorsal side 
of the clam, in a spacious pericardial chamber, the large 
heart is situated (Fig. 51, h), consisting of a median highly 
muscular ventricle surrounding the intestine and of two 
thin auricles, one on either side. From the former, two 
arteries with their numerous branches convey the blood to 
all parts of the body, where it accumulates, not in capilla- 
ries and veins, but in spaces or sinuses among the muscles 
and various organs, constituting a somewhat indefinite sys- 
tem of channels which lead to the gills and kidneys. In 
these organs the blood delivers up the waste which it has 
accumulated on its journey, and absorbing a supply of 
oxygen, it flows into the great auricles, which in turn pass 
it into the ventricle to circulate once more throughout 
the body. 

The excretory apparatus, consisting usually of two kid- 
neys, of which one may degenerate in many snails, bears a 
close resemblance to that of the annelids. In the clam, for 
instance, each consists of a bent tube symmetrically ar- 



96 ANIMAL STUDIES 

ranged on each side of the body (Fig. 51, B, &), and the inner 
ends (a), corresponding to the ciliated funnel of the anne- 
lid kidoey, open into the pericardial cavity. The walls 
are continually active in extracting wastes from the blood 
supplied to them, and these, together with the substances 
swept out from the pericardial cavity, traverse the tube and 
are carried to the exterior. In other mollusks the kidney 
may be more compact, or greatly elongated, or otherwise 
peculiar, but in reality they bear a close resemblance to 
those of the clam. 

89. Nervous system. — The nervous system, like the ex- 
cretory, differs considerably in different mollusks, yet the 
resemblances are fairly close throughout. In the clam the 
cerebral ganglia corresponding to the " brain " in annelids 
is located at either side, or above the mouth, and from it 
several nerves arise, the larger passing downward to two 
pedal ganglia ( ;;) embedded in the foot and to the visceral 
ganglia (v) far back in the body (Fig. 51, B). These nerve 
centers continually send out impulses which regulate the 
various activities of the body and also receive impressions 
from without. These come chiefly through the sense of 
touch, for in the clams the other senses are usually either 
feebly developed or altogether absent. 

90. Development. — In the mollusca new individuals al- 
ways arise from eggs, which are commonly deposited in the 
water and there undergo development. In the fresh-water 
clams the reproductive organ is usually situated in the foot 
(Fig. 51), while in the oyster and similar inactive species it is 
attached to the large adductor muscle. In these latter, and 
in many other marine forms, the eggs are shed directly into 
the sea, where they are left to undergo their development 
buffeted by winds and waves and subject to the attack of 
numerous enemies. Under such circumstances the chances 
of survival are slight, and for this reason eggs are laid in 
vast numbers, which have been variously estimated for the 
oyster, for example, from two to forty million. Develop- 



MOLLUSKS 97 

ment proceeds at first much as in the sponge, but soon the 
shell, foot, gills, and various other molluscan structures 
put in an appearance, and the few surviving young which 
have been free-swimming now settle down in some favor- 
able spot, and attach themselves or burrow according to 
their habit. 

1/ 91. Life history of fresh-water clams. — The life history of 
our common fresh-water clams is perhaps one of the most 
remarkable known among mollusks. The parent stores the 
eggs, as soon as they are laid, in the outer gill plate, and 
there, well protected, they undergo the first stages of their 
development, which results in the formation of minute 
young enclosed in a bivalve shell beset with teeth. These 
are often readily obtained, sometimes as they are escaping 
from the parent, and when examined under the microscope 
are seen to rapidly open and close their shells in a snapping 
fashion when in the least disturbed. In a state of nature 
this latter movement may result in attaching the young to 
the fins or gills of some parsing fish, which is necessary to 
its further development. Within a short time it becomes 
completely embedded in the flesh of its host, from which, 
as a parasite, it draws its nourishment, and during the 
next few weeks undergoes a wonderful series of transforma- 
tions resulting in a small mussel, which breaks its way 
through the thin skin of the fish and drops to the bottom. 
92. The gasteropods. — The gasteropods, including snails, 
slugs, limpets, and a host of related forms, fully twenty 
thousand different species in all, are found in most of our 
fresh-water streams and lakes and in moist situations on 
land, while great numbers live along the seashore and at 
various depths in the ocean, even down as far as three 
miles. Examining any of them carefully we find many of 
the same organs as in the clams, but curiously changed and 
adapted for a very different and usually active life. In our 
common land snails (Fig. 54), which we may well examine 
before passing on to a general survey of the group, the first 



ANIMAL STUDIES 



striking peculiarity is in the univalve shell, with numerous 
whorls, into which the animal may at any time withdraw 
completely. Ordinarily this is carried on the back of the 
spindle-shaped body, which is fashioned beneath into a great 




Fig. 54.— The slug (Ariolimax) and common snail (Helix). From life. 

flat sole or creeping surface that bears on its forward bor- 
der a wide opening through which mucus is continually 
issuing to enable the snail to slip along more readily. Slime 
also exudes on other points on the surface of the body and 
affords a valuable protection against excessive heat and 
drought. 

Unlike the clams, the forward end of the body is devel- 
oped into a well-marked head bearing the mouth and a 
complicated mechanism for gathering and masticating food, 
together with two pairs of tentacles, one of which carries the 
eyes. On the right side of the animal, some distance behind 
the head, is the opening of the little sac-like mantle cavity 
(Fig. 54) which contains the respiratory organs, and into 
which the alimentary canal and the kidneys pour their 
wastes. The relation of these organs to the mantle cavity 
is the same as in the clams, though the cavities differ much 
in size and position. 

93. Other snails. The shell.— Extending our acquaint- 
ance to other species of snails, we find the same general 
plan of body, although somewhat obscured at times by 



MOLLUSKS 




many modifications. A foot is generally present, also a 
more or less well-developed head, and the body is usually 
surrounded by a shell which varies widely in shape and 
size in different species. In the common limpets the early 
coiled shell is transformed into an uncoiled cap-like one, 
and in the keyhole limpets is perforated at its summit. The 

chitons or armadillo- 
snails (Fig. 55), often 
found associated with 
the limpets, carry a 
most peculiar shell con- 
sisting of eight plates, 
which enables the ani- 
mal to roll up like an 
armadillo when dis- 
turbed. A shell is by 
no means a necessity, 
however, for in many 
species, such as the 
beautiful naked snails 
or Kudibranchs (Fig. 
56) common along our coasts, it may be entirely absent, 
or, as in the ordinary slugs, reduced to a small scale em- 
bedded in the skin. 

94. Respiration. — A considerable quantity of oxygen is 
absorbed through the skin, as in all mollusks, but the chief 
part of the process is usually taken by the plume-like gills, 
one or two in number, which are located in the mantle 
cavity. In the chitons (Fig. 55) the number of gills is 
greater, amounting in some species to over a hundred, 
while in the Kudibranchs (Fig. 56) gills are absent, their 
places being taken by more or less feathery expansions of 
the skin on the dorsal surface. 

Many of the gasteropods left exposed on the rocks by a 
retreating tide retain water in the mantle cavity, from 
which they extract the oxygen until submerged again. 



Fig. 55.— The chiton, armadillo-snail or sea-cra- 
dle. The left-hand figure shows mouth in 
center of proboscis, the broad foot on each 
side of which are numerous small gills. The 
right-hand figure shows the mantle and shell, 
composed of eight plates. From life, one- 
half natural size. 



iOO ANIMAL STUDIES 

Others breathe by means of gills while under water, and by 
the surface of the body and the moist walls of the mantle 





tj§g. 


1 ,>: ''^gH^^^MHH| BBSj^awt^j^ 


^f jS\ '_i* --.,'■ '\2-~ ■■ <ft 







Fig. 56. —Three different species of naked marine snails or Nudibranchs. Natural 
size, from life. 

cavity when exposed. In some of the small Littorinas 
attached so far from the sea as to be only occasionally 
washed by the surf this latter method may prevail for days 
together — in fact they live better out of water than in it. 
It is not difficult to imagine that such forms, keeping in 
moist places, might wander far from the sea, and, losing 
their gills, become adapted to a terrestrial life. It is 
believed that in past times this has actually occurred, and 
that our land forms trace their descent from aquatic ances- 
tors. To-day they breathe by a lung — that is, they take 
oxygen through the walls of the mantle cavity, as the slug 
may be seen to do, though in some species traces of the old 
gill yet remain. 

95. Food and digestive system. — Many mollusks live upon 
seaweeds, and the greater number of terrestrial forms are 
fond of garden vegetables or certain kinds of lichens, but, 
on the other hand, the latter, together with a large number 
of marine snails, are carnivorous. In all cases the food 
requires to be masticated, and, unlike the clams, the mouth 
is usually provided with horny jaws, and an additional 



MOLLUSKS 



101 



masticatory apparatus which consists of a kind of tongue 
with eight to forty thousand minute teeth in our land 
forms (Fig. 57), while in certain marine snails they are 
beyond computation. With the licking motion of the 
tongue this rasp tears the food into shreds before it is 
swallowed, and in the whelks or borers it serves to wear a 
circular hole through the shells of other mollusks, which 

are thus killed and devoured. 
This latter process is facili- 
tated by the secretion of the 
salivary glands, which has a 
softening effect upon the 
shell. Ordinarily the saliva 
of snails exercises some di- 
gestive action. 

In the stomach of some 
snails are teeth or horny 




^C- 






w:. 




■A small portion of the radula or 
tongue-rasp of a snail (Sycotypus). 



are teem or 

ridges which also are instrumental in crushing the food, 
and in numerous minor respects peculiarities exist in differ- 
ent species according to the nature of the food ; but in its 
general features the digestive tract is similar to that of 
the clams. 

The processes of circulation and excretion are also car- 
ried on by means of systems which show a certain resem- 
blance to those of the clams. As might be expected, certain 
differences exist, sometimes very great, but they are of too 
technical a nature to concern us further. 

96. Sense-organs of lamellibranchs and gasteropoda. — 
The eyes of mollusks differ widely in their structure and 
the position they occupy in the body. In our common 
land snails two pairs of tentacles are borne on the head, 
the lower acting as feelers, while each of the upper ones 
bears on its extremity the eye, appearing as a minute black 
dot (Fig. 54). In this same position the eyes of many 
marine snails occur, but there are numerous species in 
which there are other accessory eyes. In many of the 



102 ANIMAL STUDIES 

limpets, for instance, there are numbers of additional eyes 
carried on the mantle edge just under the eaves of the 
shell, and forming a row completely encircling the body. 
(In the scallops there are two rows of brilliantly colored 
eyes, set like jewels on the edges of the mantle just within 
the halves of the shell.) In the chitons the eyes of the 
head disappear by the time the animal attains maturity, 
and in some species at least their place appears to be taken 
by great numbers of eyes, sometimes thousands, which are 
embedded in the shells. On the other hand, eyes are com- 
pletely absent in certain species of burrowing snails and in 
several living in the gloomy depths of the sea far from the 
surface ; they appear to be absent also from fresh-water 
clams ; but the fact that certain species close their shell 
when a shadow falls upon them, leads to the belief that 
while actual eyes are not present the skin is extremely 
sensitive to light. This is also the case with many snails. 

97. Smell. — Since the sense of sight is generally unde- 
veloped in the mollusks, they rely chiefly upon touch and 
smell for recognizing the presence of enemies and food. 
Tentacles upon the head and other parts of the body, and 
a skin abundantly supplied with nerves, show them to pos- 
sess a high degree of sensibility ; but in the greater num- 
ber of species the sense of smell is of chief importance. 
Many experiments show that tainted meat and strongly 
scented vegetables concealed from sight and several feet 
distant from many of our land and sea mollusks will attract 
them at once. In these forms the sense of smell appears to 
be located on the tentacles, but additional organs, possibly 
of smell, are located on various portions of the body, usu- 
ally in the neighborhood of the gills. 

98. Taste and hearing. — Several mollusks appear to be 
almost omnivorous, but others are decidedly particular in 
their choice of food, which leads us to suspect that they 
possess to some extent the sense of taste. Xerves supply- 
ing the base of the mouth have also been detected, which 



MOLLUSKS 103 

may be those of taste ; but experiments along the line are 
difficult to perform, and our knowledge of this subject is 
far from complete. The same is true of hearing. Certain 
organs, interpreted as ears and located in the foot, have 
the form of two hollow sacs, containing one or more solid 
particles of sand or lime, whose jarrings, when effected by 
sonorous bodies, may result in hearing. On the other hand, 
it is held by some that they, like the semicircular canals of 
higher animals, may regulate the muscular movements 
which enable the animal to keep its balance. 

99. Egg-laying habits and development. — The egg-laying 
habits of the gasteropods differ almost as widely as their 
haunts. The terrestrial forms lay comparatively few eggs, 
ranging in size from small shot to a pigeon's egg in some 
of the tropical species. These are buried in hollows in the 
ground or under sticks and stones, and after a few weeks 
hatch out young snails having the form of the adult. The 
same is also true of most of the fresh-water snails, which 
lay relatively smaller eggs embedded in a gelatinous mass 
frequently found attached to sticks and leaves, or on the 
walls of aquaria in which they are confined. Many marine 
species construct capsules of the most varied patterns 
which they attach to different objects, and in these the 
young are protected until they hatch. In the limpets and 
many of the chitons the eggs are laid by thousands directly 
in the water, and after a short time develop into free-swim- 
ming young, differing considerably from the parent in ap- 
pearance. Those escaping the ravages of numerous enemies 
finally settle down in a favorable situation and gradually 
assume the form of the adult. 

100. Age, enemies, and means of defense of lamellibranchs 
and gasteropods. — How much time is consumed by the young 
in growing up, and the length of time they live, are ques- 
tions generally unsettled. It is said that the oyster requires 
five years to attain maturity, and lives ten years ; the fresh- 
water clam develops in five years, and some species live from 



104 ANIMAL STUDIES 

twelve to thirty years ; and the average length of life of 
the snail appears to be from two to five years. Certain it 
is that mollusks have numerous enemies besides man which 
prevent multitudes from living lives of normal length. 
Birds, fishes, frogs, and starfishes beset them continually, 
and many fall a prey to the ravages of internal parasites or 
to other mollusks. Under ordinary circumstances the shell 
is sufficient protection, and the spines disposed on the sur- 
face in many species render the occupant still less liable to 
attack. Many snails carry on the foot a horny or calcare- 
ous plate known as the operculum, which closes the en- 
trance of the shell like a door against intruders. Certain 
noxious secretions poured out from the skin also serve as a 
means of defense, and many Xudibranchs (Fig. 56) bear 
nettle-cells on the processes of the body, which probably 
render them distasteful to many animals. Finally, there 
are numerous clams, mussels, snails, and slugs whose colors 
harmonize so closely with their surroundings that they al- 
most completely baffle detection, and enable them to lead 
as successful a life as those provided with special organs of 
defense. 

101. Cephalopods. — The animals belonging to this class, 
such as the squids and cuttlefishes (Fig. 58), are by far 
the most highly developed mollusks. They are of great 
strength, capable of very rapid movements, and several spe- 
cies are many times the largest invertebrates. In almost 
every case there is a well-defined head bearing remarkabl) 
perfect eyes, and also a circle of powerful arms provided 
with numerous suckers which aid in the capture of food 
(Fig. 58). Posteriorly the body is developed into a pointed 
or rounded visceral mass which to a certain extent is free 
from the head, giving rise to a well-marked neck. Some 
forms, such as the squids (Fig. 58, upper figure), are pro- 
vided with fins which drive the animal forward, but in com- 
mon with other cephalopods they are capable of a very rapid 
backward motion. By muscular movements water is taken 



MOLLUSKS 



105 



into the large mantle cavity within the body, a set of valves 
prevents its exit through the same channels, and upon a 
vigorous contraction of the body walls the water is forced 
out rapidlv through the small opening of the funnel,. which 









o<> <To'a^- 



Fig. 58.— Cephalopods. Lower figure, the devil-fish or octopus ( Octopus punctatus). 
The upper figure represents the squid {Loligo pealii) swimming backward by 
driving a stream of water through the small tube slightly beneath the eyes. From 
life, one-third natural size. 

drives the animal backward after the fashion of an explod- 
ing sky-rocket. In this way they usually escape the fishes 
and whales that prey upon them, but an additional device 
has been provided in the form of a sac within the body, 
whose inky contents may be liberated in such quantity as 
to cloud the water for a considerable distance, and thus 
enable them to slip away unseen into some place of safety. 
Most of the cephalopods are further protected by their 
ability to assume, like the chameleon, the color of the object 



106 ANIMAL STUDIES 

upon which they rest. In the skin are embedded multi- 
tudes of small spherical sacs filled with pigments of various 
colors, chiefly shades of red, brown, and blue, each sac be- 
ing connected with a nerve and a series of delicate muscles. 
If the animal settles upon a red surface, for example, a 
nerve impulse is sent to each of the hundreds of color sacs 
of corresponding shade, causing the muscles to contract 
and flatten the bag like a coin, and thus exposing a far 
greater surface than before, they give the animal a reddish 
hue. In the twinkling of an eye they may completely 
change to another tint, or present a mottled look, and some 
may even throw the surface of the skin into numerous 
small projections that make the animal appear part of the 
rock upon which it rests. These devices not only serve for 
protection, but they also aid in enabling these mollusks to 
steal upon their prey, chiefly fishes, which they destroy in 
great numbers with lionlike ferocity. 

The devil-fishes and a number of other species are usu- 
ally found creeping along the sea bottom, generally near 
shore, and are solitary in their habits, while the squids re- 
main near the surface and frequently travel in great com- 
panies, sometimes numbering hundreds of thousands. In 
size they usually range from a few inches to a foot or two 
in length, but a few devil-fishes and squids attain a greater 
size, some of the latter reaching the enormous length of 
from forty to sixty feet. There are many stories of their 
great strength and of their voluntarily attacking people 
and even overturning boats, but the latter are in almost 
every case sailors' yarns. 

In their external organization the cephalopods have 
little to remind one of any of the preceding mollusks, and 
their internal structure shows only a distant resemblance. 
In the Octopi (Fig. 58) the shell is lacking ; in the squid it 
is called the pen, and consists of a horn-like substance with- 
out any lime deposit ; in the cuttlefishes it is spongy and 
plate-like, and is a familiar object in the shops ; and, finally, 



MOLLUSKS 107 

in the nautilus it is coiled and of considerable size, and, un- 
like that of any other cephalopod, it is carried on the out- 
side of the animal. Interiorly it is divided by a number of 
partitions into chambers, the last one of which is occupied 
by the animal. 

The alimentary canal shows some resemblance to that 
of other mollusks, but, as in the case of the other systems 
of the body, it possesses a far higher state of development. 
The mouth is situated in the center of a circle of arms, 
which in reality are modified portions of the foot, and is 
furnished with two parrot-like jaws. From this point the 
esophagus leads back into the body mass to the stomach, 
which with the liver and intestine are sufficiently like 
those of the clam and snail to require no further comment. 

Kespiration is effected by the skin to a certain extent, 
but chiefly by two gills (four in the nautilus), and the cir- 
culatory system, which conveys the blood to and from these 
organs and over the body with its complex heart, arteries, 
capillaries, and veins, is more highly developed than in 
any other invertebrate. 

As might be expected in animals with so great sagacity 
and cunning, the nervous system and the sense-organs reach 
a degree of development but little short of what we find in 
some of the vertebrates. The chief part of the nervous 
system is located in the head, protected by a cartilaginous 
skull, a very rare structure among invertebrates ; and while 
the different ganglia may be recognized in a general way 
and be found to correspond to a certain extent to those 
of foregoing mollusks, they are so largely developed and 
massed together that it is impossible at present to under- 
stand them fully. From this point nerves pass to all 
regions of the body, to the powerful muscles, the viscera, 
and the organs of special sense, controlling the complex 
mechanism in all its workings. 

There is no doubt that the cephalopods see distinctly 
for considerable distances, and a careful examination of 



108 ANIMAL STUDIES 

the eye of the squids and cuttlefishes has shown them 
to be remarkably complex and in many respects to be 
constructed upon much the same plan as those of the 
vertebrates. As to the other senses not so much is known, 
but undoubtedly many species of cephalopods are possessed 
of a shrewdness and cunning not shared by any other 
invertebrates, save some of the insects and spiders, and are 
vastly more highly organized than their molluscan rela- 
tives. 



CHAPTER IX 

THE ARTHROPODS 

102. General characters. — In the Arthropods, that is, the 
crabs, lobsters, shrimps, insects, spiders, and a vast host 
of related forms, the body is bilaterally symmetrical, and 
is composed of a number of segments arranged in a series, 
as in the earthworm and other annelids. A hornlike cu- 
ticle, sometimes called the shell, bounds the external sur- 
face — in early life thin and delicate, but later relatively 
thick, and often further strengthened by lime salts. Along 
the line between the segments this coat of mail remains 
thin and forms a flexible joint. Appendages also are borne 
on each segment, not comparatively short and fleshy out- 
growths like the lateral appendages of many of the worms, 
but usually long and jointed (hence the name Arthropod, 
meaning jointed foot), and variously modified for many 
different uses. 

103, Classification. — The species belonging to this group 
outnumber the remainder of the animal kingdom. Their 
haunts also are most diverse. Some are adapted for lives 
in the sea and fresh water, others for widely different sit- 
uations On land, and a great number are constructed for a 
life on the wing. A certain resemblance exists among them 
all, but the modifications which fit them for their different 
habitats are also profound, and have resulted in the division 
of the Arthropods into five classes. The first class ( Crus- 
tacea) contains the crayfish, crabs, etc. ; the second ( Ony- 
chophora) includes the curious worm-like peripatus (Fig. 

109 



110 ANIMAL STUDIES 

72) ; the third (Myriapoda, meaning myriad-footed) em- 
braces the centipeds and " thousand-legs " ; the fourth 
(Insecta) contains the insects ; and the fifth (Arachnida) 
includes the scorpions, spiders, and mites. 

104. The Crustacea. — The number of species of crusta- 
ceans is estimated to be about ten thousand, and while the 
greater number of these are marine, many are found in 
fresh water and a few occur on land, in size they range 
from almost microscopic forms to the giant crabs and 
lobsters. They differ also in shape to a remarkable degree, 
but at the same time there is a decided resemblance through- 
out the group, except in those species which have become 
modified by a parasitic habit. The characteristic external 
skeleton is invariably present, and gives evidence of the 
deep internal segmentation of the body. In the simple 
Crustacea this is very apparent, but in the higher forms it 
is usually more or less obscured, owing to the fusion of some 
of the different segments, especially those of the head, as in 
the crayfish (Fig. 65). 

The class of the Crustacea is subdivided into two sub- 
classes (Entomostraca and Malacostraca), the first containing 
the fairy-shrimps {Branchipvs, Fig. 59) and their allies, the 
copepods (such as Fig. 60), the barnacles (Fig. 61), and a 
number of other species. In their organization all are com- 
paratively simple, usually small, and the appendages show 
relatively little specialization. The other subclass contains 
the more highly developed and usually large-sized Crustacea, 
among which are the shrimps, crayfishes, lobsters, crabs, 
and a number of other forms. 

105. Some simple Crustacea.— While the members of the 
first subclass are minute and inconspicuous, several species 
are often remarkably abundant in our small fresh- water 
pools. Among these is the beautifully colored fairy-shrimp 
{Brancliipas, Fig. 59), with greatly elongated body and 
leaf-like appendages, whose relatively simple character leads 
the zoologist to think that they are among the simplest 



THE ARTHROPODS 



111 



Crustacea, and in several points resemble the ancestral form 
from which all the modern species have descended. Some 
nearly related forms are provided with a great fold of the 
body-wall, which may almost completely conceal the animal 
from above, or it may be formed like a bivalve clam-shell, 
within which the entire body may be withdrawn. This 

A 




Fig. 59.— Fairy-ehrimp (Branchipus). 5, brood-pouch ; e, e?, 
compound and simple eyes ; /, paddle-shaped feet ; h, tu- 
bular heart ; i, intestine. 



latter character is also found in the water-fleas (Dap7mia) 9 
very much smaller forms, and sometimes occurring in mil- 
lions on the bottoms of our ponds and marshes. They are 
readily distinguished from the fairy-shrimp by the short- 
ness of the body, the small number of appendages, and by 
their habit of using their antennae as swimming organs, 
which gives to their locomotion a jerky, awkward character. 
106. Cyclops and relatives. — Cyclops (Fig. 60), the repre- 
sentative of a number of lowly forms belonging to the order 
of Copepods, is one of the commonest fresh-water Crustacea- 
The forward segments of the spindle-shaped body are cov- 
ered by a large shield or carapace, the feet are few in num- 
ber, and, like its fabled namesake, it bears an eye in the 
center of the forehead. Nearly related species are also re- 
markably abundant at the surface of the sea, at times occur- 



112 



ANIMAL STUDIES 



ring in such vast numbers that they impart a reddish tinge 
to the water over wide areas, and at night are largely re- 
sponsible for its phos- 
phorescence. Many oth- 
ers are parasitic in their 
habits, and scarcely a 
salt-water fish exists but 
that at one time or an- 
other suffers from their 
attacks. On the other 
hand, many fresh- and 
salt-water fishes depend 
upon the free-swimming 
forms for food, and 
hence, from an economic 
point of view, they are 
highly important organ- 
isms. 

107. Barnacles. — The 
parasitic habit and the 
lack of locomotion has 
also produced marvelous 
changes among the bar- 
nacles, so great that 
originally they were 
placed among the mol- 
lusks ; and as with the parasitic copepods, their true posi- 
tion was only known after their life-history had been de- 
termined. In the goose-barnacles * the body, attached by 
a fleshy stalk to foreign objects, is enclosed by a tough 
membrane, corresponding to the carapace of other Crus- 
tacea, in which are embedded five calcareous plates. This 




Fig. GO.— Cyclops, e. s., eggs ; i, intestine 
reproductive organ. 



* So called because of the belief, which existed for three hundred 
years prior to the present century, that when mature these animals 
give birth to geese. 



THE ARTHROPODS 



113 



is open along one side, and allows the feather-like feet to 
project and produce currents in the surrounding water 
which brings food within reach. In the acorn-barnacles 
(Fig. 61) the stalk is absent, and the body, though possess- 




Fig. 61.— Barnacles. Acorn-barnacles chiefly in lower part of figure ; goose-barnacles 
above. Natural size. 

ing the same general character as the goose-barnacles, is 
shorter, and enclosed in a strong palisade consisting of six 
calcareous plates. 

The larger number of barnacles attach themselves to 
the supports of wharves, the hulls of ships, floating tim- 
bers, the rocks from the shore-line down to considerable 
depth, and a few species occur on the skin of sharks and 
whales. On the other hand, there are several species which 
are parasitic, and in accordance with this mode of life ex- 
hibit various degrees of degeneration. In the most extreme 



114 ANIMAL STUDIES 

cases (Sacculina) the sac-like body, attached to the abdo- 
men of crabs, is entirely devoid of appendages and any 
signs of segmentation. A root-like system of delicate fila- 
ments extends from the exposed part of the animal into 
the host and absorbs the necessary nutriment. The mouth 
and alimentary canal are accordingly absent — in fact, the 
body contains little but the reproductive organs and a very 
simple nervous system. 

108. Structure. — In the internal organization of these 
smaller crustaceans many differences may be noted, though 
they are usually less profound than the external. Ordi- 
narily the alimentary canal is a straight tube passing 
through the body, and is provided with a poueh-like 
stomach, and a more or less clearly defined liver. In 
all, except the parasitic species, the external mouth-ap- 
pendages masticate the food, and in a very few of the 
above-described groups it may be further ground between 
the horny ridges on the stomach-walls. After this pre- 
liminary treatment it is subjected to the action of the 
digestive juices, and when liquefied is absorbed into the 
body. Here it is circulated by a blood-system of widely 
different character. In many cases definite arteries and 
veins are absent. The blood courses through the body in 
the spaces between the different organs propelled by the 
beating of the heart, which it is made to traverse. In 
Cyclops (Fig. 60) even the heart is absent, and the blood 
is made to circulate by contractions of the intestine. In 
most of these smaller Crustacea considerable oxygen is ab- 
sorbed through the body-wall; but in several species, for 
example, the fairy-shrimp (Fig. 59), special gills are devel- 
oped on the appendages of the body. 

109. Multiplication. — Among the Crustacea thus far con- 
sidered the males are usually readily recognized owing to 
their small size. The females also are usually provided 
with brood-pouches in which the developing eggs are pro- 
tected. In almost every case the young are born in the 



THE ARTHROPODS 



115 



form of minute larvae, provided with three pairs of append- 
ages, a median eye (Fig. 62), and a firm external skeleton 
or cuticle. This latter prevents the continuous growth of 
the larvae or nauplius, and every few days it is thrown off, 
and while the new one is forming the body enlarges. Dur- 
ing this time new appendages are developed, so that after 
each moult the young crusta- 
cean emerges less like its 
former self and more and more 
like its parents. In the bar- 
nacles, after several moults 
have taken place, the young 
become permanently attached 
by means of their first anten- 
nae, their thoracic feet change 
into feathery appendages, and 
several other changes occur. 
In some of the parasitic bar- 
nacles (Sacculina) the larva 
attaches itself to a crab, throws 
off its various appendages, and, 
after other great degenerative 
changes, enters its host. For 
a time, therefore, their development is toward greater com- 
plexity, but the later stages constitute a retrograde meta- 
morphosis. 

110. More complex types. — The larger, more useful, and 
usually more familiar Crustacea belong to the second divi- 
sion (subclass Malacostraca). It comprises such animals as 
the shrimps, crayfish, lobsters, crabs, and a number of other 
forms which are at once distinguished from the preceding 
by the constant number of segments composing the body. 
Of these, five constitute the head, eight the thorax, and 
seven the abdomen. The head segments are always fused 
together, and with them one or more thoracic segments 
unite to form a more or less complete cephalothorax. Also, 




Fig. 62.— Development of a barnacle 
(Lepas). a, larva ; b, adult. 



116 ANIMAL STUDIES 

some of the head segments give rise to a great fold of the 
body-wall, the carapace, which extends backward and covers 
all or a part of the thorax, with which it may firmly unite, 
as in the crayfish. The appendages are usually highly spe- 
cialized, and are made to perform a variety of functions. 

111. The shrimps. — Among the simplest of these are the 
opossum-shrimps (Fig. 63) and their relatives, small trans- 




Fig. 63.— The opossum-shrimp (Jlysis americana). 

parent creatures often seen swimming in great numbers at 
the surface of the sea or hiding among the seaweeds along 
the shore. In general appearance they resemble crayfishes 
or prawns, but are readily distinguished by the two-branched 
thoracic feet. This " split-foot " character also occurs 
among many of the preceding Crustacea, and is generally 
a badge of low organization, tending to disappear in the 
more highly organized forms. In this and other respects 
the shrimps are especially interesting in their relation to 
the preceding Crustacea, and in the fact that they may 
closely resemble the ancestors of the modern prawns (Fig. 
64), lobsters, crayfishes, and crabs. 

112. Crayfishes and lobsters. — The last-mentioned spe- 
cies and their allies, usually large and familiar forms, con- 
stitute a group known as the decapods (meaning ten feet), 
referring to the number of thoracic feet. Among the mem-^ 
bers of this division probably none are more familiar than 
the crayfishes, which occur in most of the larger rivers and 
their tributaries throughout the United States and Europe. 
It is their habit to remain concealed in crevices of rocks 



THE ARTHROPODS 



117 



or in the mouths of the burrows which they excavate, and 
from which they rush upon the small fish, the larva3 of 




Fig. 6-1.— Prawn (Ileptacarpus brevirostris). 



many animals, and other equally defenseless creatures 
which constitute their bill of fare. In turn they are 
eagerly sought by certain birds and four-footed animals, and, 
especially in France, 
are extensively used for 
food by man. 

Closely related to 
the crayfishes and dif- 
fering but little from 
them structurally are 
the lobsters. In this 
country they are con- 
fined to the rocky coasts 
from JS T ew Jersey to 
Labrador, living upon 
fish, fresh or otherwise, 
various invertebrates, 
and occasionally sea- 
weeds. Ear more than 
the crayfish, the lobster 
is in demand as an arti- 
cle of food. By the aid 
of nets or various traps 




Fig. 65.— The crayfish {Astacus). 



118 ANIMAL STUDIES 

millions are caught each year, and to such an extent has 
their destruction proceeded that in many places they are 
well-nigh exterminated. At the present time, however, leg- 
islation, numerous hatcheries, and a careful study of their 
life habits is doing much to better matters and inciden- 
tally to put us in possession of many interesting zoological 
facts along this line, some of which will be mentioned later. 
Frequently the prawns, especially the larger ones, and a 
spiny lobster (Palinurus), are mistaken for crayfishes or 
lobsters, but they differ from them in the absence of the 
large grasping claws. 

Along almost any coast some of these animals are to be 
found, often beautifully colored and harmonizing with the 
seaweeds among which they live, or so transparent that 
their internal organization may be distinctly seen. Farther 
out at sea other species swim in incredible numbers, feed- 
ing upon minute organisms, and in turn fed upon by numer- 
ous fishes and whales ; and, especially on the Pacific coast, 
shrimp-fishing is an important industry. 

113. The hermit-crabs. — The last of these long-tailed 
decapods is the interesting group of the hermit-crabs, 
which occur in various situations in the sea. In early life 
they take possession of the empty shell of some snail, and 
the protected abdomen becomes soft and flabby, while the 
appendages in this region almost completely disappear. 
The front part of the body, on the other hand, continually 
grows in firmness and strength, and is admirably adapted 
for the continual warfare which these forms wage among 
themselves. As growth proceeds the necessity arises for a 
larger shell, and the crab goes " house-hunting " among the 
empty shells along the shore, or it may forcibly extract the 
snail or other hermit from the home which strikes its fancy. 

Many of the hermit-crabs enjoy immunity from the 
attacks of their belligerent relatives by allowing various 
hydroids to grow upon their homes. Others attach sea- 
anemones to their shells or to one of their large claws, 



THE ARTHROPODS 



119 



which they poke into the face of any intruder. While 
the anemones or hydroids are made to do valiant service 




Fig. 66.— Hermit-crab (Pagurus bernhardus) in snail shell covered with Hydractinia. 

with their nettle-cells, they also enjoy the advantages of 
a large food-supply which is attendant upon the free ride. 

114. The crabs. — The most highly developed Crustacea 
are the crabs or short-tailed decapods which abound between 
tide-marks alongshore, and in diminishing numbers extend 
to great depths. The cephalothorax is usually relatively 
wide, often wider than long, and the greatly reduced abdo- 
men is folded against the under side of the thorax. Corre- 
lated with the small size of the abdomen, the appendages 
of that region disappear more or less, but the remaining 
appendages are similar to those of the crayfish or lobsters. 
All these different parts, however, are variously modified in 
each species to fit it for its own peculiar mode of life. In 
some forms, such as the common cancer-crab (Fig. 67), the 
legs are comparatively thick-set and possessed of great 
strength, enabling them to defend themselves against most 
enemies. On the other hand, there are the spider-crabs 
with small bodies and relatively long legs, withal weak, and 



120 



ANIMAL STUDIES 



yet so harmonizing with their surroundings that they are 
as likely to survive as their stronger relatives. In this 




Fig. 67.— Kelp-crab (Epialtus produchis) in upper part of figure; to the right the 
edible crab (Cancer productus), and the shore-crab (Pugellia richii). 

connection it is interesting to note that the giant crab of 
Japan, the largest crustacean, being upward of twenty feet 
from tip to tip of the legs, is a spider-crab, constructed on 




Fig. 68.— The fiddler-crab (Gelasimus). Photograph by Miss Mart Rathbun 



the same general pattern as our common coast forms. 
Between these two extremes numberless variations exist, 



THE ARTHROPODS 



121 



some for known reasons, but more often not readily under- 
stood. And not only does the form vary, but the external 
surface may be sculptured or beset with spines or tubercles 
which frequently render the animal inconspicuous amid its 
natural surroundings. Such an effect is heightened by the 
presence of sponges, hydroids, and various seaweeds which 
the crab often permits to gather upon its body. 

115. Pill-bugs and sandhoppers. — Finally there remain the 
groups of the pill- or sow-bugs (Isopods) and the sand-fleas 
or sandhoppers (Amphipods). In the first of these the 
body is usually small and compressed, the thorax more or 
less plainly segmented, and the seven walking (thoracic) 
legs are similar. In the female each leg bears at its base a 
thin membranous plate which extends inward and hori- 




Fig. 69.— Isopod or pill-bug {Porcellio laevis). 

zontally, thus forming on the under side of the body a 
brood-pouch (Fig. 69) in which the young develop. As 
one may readily discover in any of the common species, 
the abdominal segments are more or less fused, and bear 
appendages adapted for respiration and, in the aquatic 
forms, for swimming. 
9 



122 



ANIMAL STUDIES 



The marine isopods occur in the sand, under rocks, and 
in the seaweeds ; many are parasitic upon fishes ; and the ter- 
restrial forms (Fig. 69) are very common objects under old 




Fig. 70.— Amphipods or sand-fleas (Gammarus, upper species, and Capretta). 



logs and in cellars, where they live chiefly on vegetable mat- 
ter. In the sand-fleas the body is compressed from side to 
side, and while the thorax shows distinct segments, the legs 
are frequently dissimilar, and some may bear pincers. One 
of their most distinctive marks concerns the last three ab- 
dominal appendages, which are usually modified for leaping. 
The sand-fleas (Fig. 70) are familiar objects to any one 
who has collected along the beach and has turned over the 
cast-up seaweeds, while numbers of small species often oc- 
cur among the plants in our fresh-water ponds. Some most 
curious and highly modified forms, whose general appear- 
ance is shown in the lower part of Fig. 70, occur among 



THE ARTHROPODS 123 

hydroid colonies, with which their bodies harmonize in 
form and color. And, lastly, most bizarre creatures, known 
as " whale-lice," attach themselves to the skin of whales, of 
which each species acts as host for one or more kinds. 

116. Internal organization. — Most Crustacea are carnivo- 
rous, preying upon almost any of the smaller animals within 
convenient reach ; a much smaller number live on vege- 
table food ; and there are many, such as the crayfishes, lob- 
sters, and numerous crabs, which are also notorious scaven- 
gers. In these latter forms the food is held in one of the 
large pincers, torn into shreds by the other, and transferred 
to the mouth-parts, where, as in all Crustacea, it is soon 
reduced to a pulp by their rapid movements. In many 
species the food is now ready for the digestive process, 
but not so in the higher forms. If the stomach of any of 
these, for example, the crabs or crayfishes, be opened, three 
(Fig. 71, s) large teeth operated by powerful muscles will 
be noted, and beyond these a strainer consisting of many 
closely set hairs. In operation this "gastric mill" takes 
the food passed on from the mouth-parts, and crushes and 
tears it until fine enough to pass through the strainer, 
whereupon it is dissolved by the juices from the liver and 
is absorbed as it passes down the intestine. 

The circulatory system is usually highly developed, and 
consists of a heart, in some species almost as long as the 
body, though usually shorter (Fig. 71), from which two or 
more arteries branch to all parts of the body. Here the 
blood, instead of emptying into definite veins, pours into a 
series of spaces or sinuses in among the muscles and other 
organs of the body, through which it makes its way back to 
the heart. During this return journey it is usually made 
to traverse definite respiratory organs, either situated upon 
the legs or, as feathery outgrowths, upon the sides of the 
body, and generally concealed under the carapace. A por- 
tion of the blood is also continually sent to the kidneys, 
which are located either at the base of the second antennas 



124 ANIMAL STUDIES 

(and known as green glands), as in the crayfishes or crabs, 
or on the second maxillae (shell-glands) in many of the 




Fig. 71.— Dissection of crayfish, b, brain ; h, heart ; i, intestine ; k, kidney ; I, liver ; 
n, nerve-cord ; r, reproductive organ ; s, stomach, showing two teeth in position. 

simpler crustaceans. Their method of operation is much 
like that of the kidneys in the earthworm. 

117. Nervous system and special senses. — The nervous sys- 
tem also shows a decided resemblance to that of the anne- 
lids. The cerebral ganglia or brain is situated above the 
alimentary canal in the head, and connects with the ven- 
trally lying cord by a collar. As in the earthworm, this 
ventral cord is double, and bears a pair of swellings or gan- 
glia in each segment. In the crayfish, crabs, and other 
highly modified forms, where the segments tend to fuse,' 
several of these ganglia may also unite, and except in early 
life their number cannot be determined. 

Among the less specialized Crustacea the order of intel- 
ligence is low, though perhaps it may prove to be higher 
than is usually supposed when such forms have been more 
thoroughly studied. The following quotation relating to 
the lobster applies even more to the higher forms, the 
crabs : " Sluggish as it often appears when out of water and 
when partially exhausted, it is quite a different animal when 
free to move at will in its natural environment on the sea- 



THE ARTHROPODS 125 

bottom. It is very cautious and cunning, capturing its 
prey by stealth, and with weapons which it knows how to 
conceal. Lying hidden in a bunch of seaweed, in a crevice 
among the rocks, or in its burrow in the mud, it waits until 
its victim is within reach of its claws, before striking the 
fatal blow. The senses of sight and hearing are probably 
far from acute, but it possesses a keen sense of touch and 
of smell, and probably also a sense of taste." 

Although enclosed in a horny and often very thick and 
strong armor, the sense of touch is very keen in the 
Crustacea and in arthropods generally. On many of the 
more exposed portions delicate hairs or pits connected 
with the nervous system occur in great abundance. Some 
of these, usually on the antennae, undoubtedly serve in 
detecting odors, but the remainder are considered to be 
tactile. In the higher Crustacea, such as the crayfish, 
lobsters, and crabs, ears are usually found, consisting of 
sacs lined with similar delicate hairs, and containing sev- 
eral minute grains of sand, which in many cases make their 
way through the small external opening. Vibrations com- 
ing through the water gently shake the grains of sand, 
causing them to strike against the hairs which communi- 
cate with the nervous system — a very simple ear, yet suffi- 
cient for the needs of the animals. 

The eyes of the Crustacea and arthropods in general are 
either simple or compound. The simple and frequently 
single eyes usually consist of a relatively few cells embedded 
in a quantity of pigment and connected with the nervous 
system. It is doubtful whether they perceive objects as 
anything more than highly blurred images, and perhaps 
they merely recognize the difference between light and 
darkness. The compound eyes, on the other hand, are 
remarkably complex structures, often borne on the tops of 
movable stalks, as in the common crabs and crayfishes. 
Each consists of an external transparent cornea, divided 
into numerous minute hexagonal areas corresponding to as 



126 ANIMAL STUDIES 

many internal rods of cells, provided with an abundant 
nerve-supply. These latter elements may perhaps repre- 
sent simple eyes grouped together to form the compound 
one ; and it appears possible that each element may form 
a complete image of an object, as each of our eyes is known 
to do. On the other hand, many hold that the complete 
eye forms only one image, a mosaic, each element con- 
tributing its share. 

118. Growth and development. — As we have seen, the 
simpler Crustacea hatch as minute larvae (Fig. 62), and dur- 
ing their growth to the adult condition are especially sub- 
ject to the attacks of multitudes of hungry enemies. In 
the higher forms, such as the crabs, some of these early 
transformations take place while the young are still within 
the egg and attached to the parent. Accordingly, the little 
ones are fairly similar to their parents, and their later his- 
tory is very well exemplified by the lobster. 

The eggs of the lobster are most frequently hatched in 
the summer months, usually July, after they have been 
carried by the parent for upward of a year. The young, 
about a third of an inch in length, at once disperse, undergo 
four or five moults during the next month, then, ceasing 
their swimming habits, settle to the bottom among the 
rocks. At this time, twice their original size, they closely 
resemble their parents, and their further development is 
largely an increase in size. " The growth of the lobster, 
and of every arthropod, apparently takes place, from in- 
fancy to old age, by a series of stages characterized by the 
growth of a new shell under the old, by the shedding of 
the outgrown old shell, a sudden increase in size, and the 
gradual hardening of the shell newly formed. Not only is 
the external skeleton cast off in the moult and the linings 
of the masticatory stomach, the esophagus, and intestine, 
but also the internal skeleton, which consists for the most 
part of a complicated linkwork of hard tendons to which 
muscles are attached." 



THE ARTHROPODS 



127 



119. Peripatus (class Onychophora). — It is generally be* 
lieved that the Crustacea, insects, and spiders, together 
with their numerous relatives, trace their ancestry back to 
animals that bore a certain resemblance to the segmented 
worms. Most of these ancient types have 
long been extinct, but here and there 
throughout the earth we occasionally meet 
with them. 

Among the most interesting of these 
are a few widely distributed species belong- 
ing to the genus Perijmtus (Fig. 72), but as 
they are comparatively rare we shall dis- 
miss them with a very brief description. 
They usually dwell in warm countries, un- 
der rocks and decaying wood, emerging at 
night to feed on insects, which they ensnare 
in the slime thrown out from the under 
surface of the head. Their external form, 
their excretory system, and. various other 
organs are worm-like. On the other hand, 
the appendages are jointed, and one pair 
has been modified into jaws. The peculiar 
breathing organs characteristic of the in- 
sects are also present. Peripatus therefore 
gives us an interesting link between the 
worms and insects, and also affords an idea 
of the primitive insects from which the 
modern forms have descended. 

120. The centipeds and millipeds (class 
Myriapoda). — Many of the myriapods — that 
is, the centipeds and thousand-legged worms 
— are familiar objects under logs and stones 
throughout the United States. The first of these (Fig. 73) 
are active, savage creatures, devouring numbers of small 
animals, which they sting by means of poison-spines on the 
tips of the first pair of legs. The bite of the larger tropical 



&£§£S' 




Fig. 72.— Peripatus 
{Peripatus eiseni). 
Twice the natural 
size. 



128 



ANIMAL STUDIES 



species especially causes painful but not fatal wounds in 
man. 

On the other hand, the millipeds (Fig. 74) or thousand- 
legs are cylindrical, slow-going animals, feeding on vegetable 





Fig. 73.— Centiped. 
One-half natural size. 



Fig. 74.— Thousand-legs or milliped (Julus). 
Natural size. 



substances without causing any particular damage, except 
in the case of certain species, which work injury to crops. 
"When disturbed they make little effort to escape, but roll 
into a coil and emit an offensive-smelling fluid, which ren- 
ders them unpalatable to their enemies. 

All present a great resemblance to the segmented worms, 
as their popular names often testify; but, on the other 
hand, many points in their organization indicate a closer 
relationship to the insects. As in the latter, the head is 
distinct, and bears a pair of antennae, the eyes, and two or 
three pairs of mouth-parts. The trunk is more worm-like, 
and consists of a number of similar segments, each bearing 



THE ARTHROPODS 129 

one or two pairs of jointed legs. In their internal organ- 
ization the character of the various systems closely resem- 
bles that of the insects, and will be more conveniently 
described in that connection. 

Among the myriapods the females are usually larger 
than the males. Some of the centipeds deposit a little 
mass of eggs in cavities in the earth and then abandon 
them, while others wrap their bodies about them and pro- 
tect them until the young are hatched. The millipeds lay 
in the same situations, but usually plaster each egg over 
with a protective layer of mud. After several weeks the 
young appear, often like their parents in miniature, but in 
other species quite unlike, and requiring several molts to 
complete the resemblance* 



CHAPTER X 

ARTHROPODS (Continued). CLASS INSECTS 

121. Their numbers. — It has been estimated that upward 
of three hundred thousand named species of insects are 
known to the zoologist, and that these represent a fifth, or 
possibly a tenth, of those living throughout the world. Many 
of these species, as the may-flies and locusts, are represented 
by millions of individuals, which sometimes travel in such 
great swarms that they darken the sky. With nearly all 
of these the struggle for existence is fierce and unrelenting, 
and it is little wonder that such plastic animals have 
changed in past times and are now becoming modified in 
order to adapt themselves to new situations where food is 
more abundant and the conditions less severe. Owing to 
such modifications we find some species fitted for flying, 
others for running and leaping, or for a life underground, 
and many for a part or all of their lives are aquatic in their 
habits. 

122. External features. — The body of an insect — the 
grasshopper, for example — consists of a number of rings 
arranged end to end, as we have seen them in the Crustacea 
and the segmented worms. In the abdomen these are 
clearly distinct, but in the thorax, and especially the head, 
they have become so intimately united that their number 
is a matter of uncertainty. These three regions — head, 
thorax, and abdomen — are usually clearly defined in most 
insects, but they are modified in innumerable ways in ac- 
cordance with the animal's mode of life. 

130 



ARTHROPODS. CLASS INSECTS 131 

The head usually carries the eyes, a pair of feelers (an- 
tennae), and three pairs of mouth-parts which may be fash- 
ioned into a long, slender tube to be used in sucking, and 
frequently as a piercing organ ; or they may be constructed 
for cutting and biting. The thorax bears three pairs of 
legs and usually two pairs of wings ; sometimes one pair or 
none. The appendages of the abdomen are usually small 
and few in number, or even absent. 

123. Internal anatomy. — The restless activity of insects 
is proverbial. Some appear to be incessantly moving about, 
either on the wing or afoot, and are endowed with com- 
paratively great strength. Ants and beetles lift many times 
their own weight. Numerous insects are able to leap many 
times their own length, and others perform different kinds 
of work with a vigor and rapidity unsurpassed by any other 
class of animals. As is to be expected, the muscular sys- 
tem is well developed, and exhibits a surprising degree of 
complexity. Over five hundred muscles are required for 
the various movements of our own bodies, but in some of 
the insects more than seven times this number exist. The 
amount of food necessary to supply this relatively immense 
system with the required nourishment is correspondingly 
large. Many insects, especially in an immature or larval 
condition, devour several times their own weight each day. 
Their food may consist of the juices of animals or plants, 
which they suck out, or of the firmer tissues, which are 
bitten or gnawed off. 

Not only do the mouth-parts stand in direct relation to 
the habits of the animal and to its food, but, as we have 
often noticed before, the internal organization is also 
adapted for the digestion and distribution of the nutritive 
substances in the most economical way. For this reason 
we find the alimentary canal differing widely in the various 
forms of insects. In each case it extends from the mouth 
to the opposite end of the animal, and ordinarily consists 
of a number of different parts. In the insect shown in 



132 



ANIMAL STUDIES 



M.c 



Fig. 75 the mouth soon leads into the esophagus, which 
in turn leads into the crop that serves to store up the food 
until ready for its entry into the stomach; or in some of 
the ants, bees, and wasps it may contain material which 

may be disgorged and fed 
to the young. In many 
cases the stomach is small 
and ill-defined as in Fig. 75, 
and again it may reach 
enormous dimensions, near- 
ly filling the body. It may 
also bear numerous lobes or 
delicate hair-like processes, 
which afford a greater sur- 
face for the absorption of 
food. Behind the stomach 
are a number of slender 
outgrowths that are believed 
to act as kidneys. Beyond 
their insertion lies the in- 
testine, which, like the 
stomach, is the subject of 
many modifications in the 
different kinds of insects. 
The digested food is rap- 
idly absorbed through the coats of the stomach and intes- 
tine and enters a circulatory system which reminds us of 
what exists in many of the Crustacea. The heart is situ- 
ated above the digestive tract, and from it arteries pass out 
to different parts of the body. Here the blood leaves the 
vessels and is poured directly into the spaces among the 
viscera, whence it is finally conducted through irregular 
channels to the heart by its pulsations. 

In the Crustacea the blood is made to pass through a 
respiratory system usually in the form of definite gills, and 
the oxygen with which it is charged is distributed to all 




Fig.. 75.— Cockroach, dissected to show ali- 
mentary canal, at. c— After Hatschek 
and Cori. 



ARTHROPODS. CLASS INSECTS 133 

parts of the body. In the insects the blood serves almost 
entirely to carry the food, and the oxygen is conveyed 
through the animal by a remarkable contrivance found 
only in the insects, the spiders, and a few related forms. 

124. Respiratory system. — If we examine an insect, the 
grasshopper for example, Ave find a number of small brown 
spots on each side of the abdomen, each of which under a 
magnifying-glass is seen to be perforated by a narrow slit. 
Carefully opening the body, we find that each slit is in 
communication with a white, glistening tube that rapidly 
branches and penetrates to all parts of the animal. When 
the body is expanded the air rushes into the outer openings, 
on through the open tubes, and is distributed with great 
rapidity to all the tissues of the body. In many insects 
some of these tubes connect with air-sacs which probably 
serve to buoy up the insect during its. flights through 
the air. 

125. Wingless insects (Aptera). — The simplest of all in- 
sects are the fishmoths and springtails, relatively small 
organisms covered with shining scales or hairs. The first 
of these is occasionally seen running about in houses feed- 
ing upon cloth and other substances, while the latter live 
in damp places under stones and logs. They are without 
wings, but are able to run rapidly and to leap considerable 
distances. In addition to the ordinary appendages, the 
abdomen bears what are perhaps rudimentary legs, a fact 
which, together with their relatively simple structure, 
strengthens the belief that the insects have descended 
from centiped-like ancestors. 

126. Grasshoppers, crickets, katydids, etc. (Orthoptera). — 
Rising higher in the scale of insect life, we arrive at the group 
of the cockroaches, crickets, grasshoppers, locusts, and 
other related insects. Four wings are present, the first pair 
thickened and overlapping the second thinner pair. The 
latter are folded lengthwise like a fan, which is said to have 
given the name Orthoptera (meaning straight-winged) to 



134 ANIMAL STUDIES 

this group of insects. These extend all over the world, 
being particularly abundant in the warmer countries, and 
their strong biting mouth-parts and voracious appetites 
render many of them dreaded pests to the farmer. The 
cockroaches are nocturnal in their habits, racing about at 
night, devouring victuals in the pantry and gnawing the 
bindings of books. During the day their flat bodies enable 
them to secrete themselves in crevices wherever there is 
sufficient moisture. 

In the grasshoppers, locusts, katydids, and crickets the 
body is more cylindrical, and the hind pair of legs are often 
greatly lengthened for leaping. The crickets and katydids 

are nocturnal, the former re- 
maining by day in burrows 
which they construct in the 
earth, the latter resting qui- 
etly in the trees. At night 

Fig. 76.— The Rocky Mountain locust.— , -, « , ■, 

After Riley, from The Insect World. they feast Upon Vegetable 

matter principally, though 
some species are known to prey on small animals. Those 
insects we usually term grasshoppers (properly called lo- 
custs) are specially destructive to vegetation. Some spe- 
cies are strong fliers, and this, connected with their abil- 
ity to multiply rapidly, renders them greatly dreaded pests. 
They have been described as flying in great swarms, form- 
ing black clouds, even hiding the sun as far as the eye 
could reach. The noise made by their wings resembled 
the roar of a torrent, and when they settled upon the earth 
every vestige of leaf and delicate twig soon disappeared. 

The eggs of the majority of Orthoptera are laid in the 
ground, where they frequently remain through the winter. 
When hatched the young quite closely resemble the parents, 
and, after a relatively slight metamorphosis, assume the 
adult form. 

127. Dragon-flies, may-flies, white ants, etc.— The dragon-, 
caddis-, may-flies, ant lions, and the white ants possess four 




ARTHROPODS. CLASS IXSECTS 135 

thin and membranous wings incapable of being folded. 
These possess a network of delicate nervures, giving the 
general name nerve- winged insects' to these various small 
orders. Of the forms mentioned above, all but the white 
ants lay their eggs in the water, and the developing larvae 




Fig. 77.— Dragon-fly (Libellula pulchetta). 

spend their lives in this medium until the time comes for their 
complete metamorphosis into the adult. The larvae of the 
caddis-flies protect themselves within a tube of stones or sticks 
bound together with silken threads, which they usually 
attach to the under side of stones in running water. On 
the other hand, the young of the dragon- and may-flies, pro- 
vided with strong jaws, are active in the search of food and 
very voracious. In time they emerge from their larval skin 
and the water in which they live, and after a life spent on 
the wing they deposit their eggs and perish. The adult 
ant-lion, a type of the related order (Neuroptera), which 
has somewhat the appearance of a small dragon-fly, lays its 
eggs in light sandy soil. In this the resulting larvae exca- 
vate funnel-shaped pits, at the bottom of which they lie con- 



136 



ANIMAL STUDIES 



cealed. Insects stumbling into their pitfalls are pelted with 
sand, which the ant-lion throws at them with a jerky motion 
of the head, and are speedily tumbled down the shifting 
sides of the funnel to be seized and devoured. 

While the white ants are not in any way related to the 
true ants, they possess many similar habits. Associated in 
great companies, they excavate winding galleries in old logs 
and stumps, and, further, are most interesting because of 
the division of labor among the various members. The 
wingless forms are divided into the workers, which exca- 
vate, care for the young, and otherwise labor for the good 
of the others; and into the soldiers, huge-headed forms, 




Fig. 78. — Ant-lion larva plowing its way through the sand (upper figure) while an- 
other is commencing the excavation of a funnel-shaped pit similar to one on right. 
Photograph by A. L. Melandeb and C. T. Brues. 

whose strong jaws serve to protect the colony. The re- 
maining winged forms are the kings and queens. In the 
spring many of the royalty fly away from home, shed their 
wings, unite in pairs, and set about to organize a colony. 
The queen rapidly commences to develop eggs, and in some 



ARTHROPODS. CLASS INSECTS 



137 



species her body becomes so enormously distended with 
these that she loses the power of locomotion and requires 
to be fed. A single queen has been known to lay eggs at 
the rate of sixty per minute (eighty thousand a day), and 




Fig. 79.— Termites or white ants, a, queen ; b, winged male ; c, worker ; d, soldier. 

those destined to royal rank are so nursed that they advance 
farther in their development than the remaining sterile 
and wingless forms. 

128. The bugs (Hemiptera). — The large and varied group 
of the bugs {Hemiptera) includes a number of semi-aquatic 
species, such as the water-boatmen, often seen rowing 
themselves along in the ponds by means of a pair of oar- 
shaped legs, in search of other insects. Somewhat similar 
at first sight are the back-swimmers, with like rowing 
habits, but unique in swimming back downward. Both of 
these bugs frequently float at the surface, and when about 
to undertake a subaquatic journey they may be seen to 
imprison a bubble of air to take along. Closely related are 
the giant water-bugs (Fig. 80), which often fly from pond 
to pond at night. In such flights they are frequently 
10 



138 



ANIMAL STUDIES 



VbJk^W 



attracted by lights, and have come to be called " electric- 
light bugs." 

Among our most dreaded insect pests are the chinch- 
bugs — small black-and-white insects, but traveling in com- 
panies aggregating man}- millions. 
As they go they feed upon the 
stems and leaves of grain, which 
they devour with extraordinary ra- 
pidity. The squash-bug family is 
also extensive, and destructive to 
the young squash and pumpkin 
plants in the early spring. 

The lice are small, curiously 
shaped bugs, which suck the blood 
of other animals. The plant-lice, 
also small, suck the juices of 
plants, and are often exceedingly 
dostructive. This is especially true 
of the phylloxera, a plant-louse 
which causes annually the loss of 
millions of dollars among the vine- 
yards of this and other countries. 
Even more destructive are the scale-insects, curiously mod- 
ified forms, of which the wingless females may be found on 
almost any fruit-tree and on the plants in conservatories, 
their bodies covered with a downy, waxy, or other kind of 
covering, beneath which they remain and lay their eggs, 

129. The flies (Diptera).— The group of the Diptera 
(meaning two-winged) includes the gnats, mosquitoes, fleas, 
house-flies, horse-flies (Fig. 81), and a vast company of 
related forms. Only a single pair of wings is present, the 
second pair being rudimentary or fashioned into short, 
thread-like appendages known as balancers, though they 
probably act as sensory organs and are not directly con- 
cerned with flight. The mouth-parts are adapted for pier- 
cing and sucking. The eyes, constructed on the same plan 




Fig. £0.— Giant water-bug (Ser- 
phus dilatatus), with eggs at- 
tached. 



ARTHROPODS. CLASS INSECTS 



139 




Fig. 81.— Horse-fly (Therio- 
plectes). 



as those of the Crustacea, are comparatively large, and are 
frequently composed of a great number of simple eyes 
united together, upward of four 
thousand forming the eye of the 
common house-fly. 

These insects are widely distrib- 
uted throughout the world, where 
they inhabit woods, fields, or houses 
as best suits their needs. Their 
food is varied. Some suck the 
juices of plants, others attack ani- 
mals, and, while many are trouble- 
some pests, others, especially in the 
early stages of their existence, are 
of great benefit. 

130. Typical forms. — Owing to 
the widely different habits and 
structure of the members of this group, we shall briefly 
consider two examples, the mosquito and the house-fly, 
which will give us a fairly good idea of the characteristics 
of all. The eggs of the mosquito are laid in sooty-look- 
ing masses on the surface of stagnant pools. Within a 
very short time the young hatch, and, owing to their pecul- 
iar swimming movements, are known as "wrigglers." They 
are then active scavengers, devouring vast quantities of 
noxious substances and performing a valued service. They 
frequently rise to the surface, take air into the tracheal 
system, which opens at the posterior end of the body, and 
descend again. After an increase in growth and many in- 
ternal changes resulting in a chrysalis-like stage, they rise 
to the surface, split the shell, and, using the latter as a float, 
carefully balance themselves and soon fly away. 

The house-fly usually lays its eggs in decaying vegetable 
matter, and the young, maggot-like in form, are active 
scavengers. They too undergo deep-seated changes during 
the next few days, finally transforming into the adult. 



140 



ANIMAL STUDIES 



Many of this great group of the flies spend their early life 
in the water or other medium acting as scavengers ; but, on 
\,he other hand, numbers attack domestic and other animals, 
and throughout their entire lives are an intolerable plague. 
131. The beetles (Coleoptera).— Owing to the ease of pres- 
ervation and their bright colors, the beetles have probably 
been more widely collected than other insects. Fully ten 




Fig. 82.— Long-homed borer {Ergates). Larva (left-hand figure), pupa, and adult 
insect. 



thousand distinct species are known in Xorth America 
alone. They are all readily recognized by the two firm, 
horny sheaths enclosing the two membranous wings, which 
alone are organs of flight. The mouth is provided with 
jaws, which are used in gnawing. Some prey on noxious 
insects or upon decaying vegetable or animal matter, and 
are often highly beneficial ; but others attack our trees and 
domestic animals, and work incalculable damage. 



ARTHROPODS. CLASS INSECTS 141 

In some of the stag- or wood-beetles (Fig. 82), which 
we may select as types, the adults are often found crawling 
about on or beneath the bark of trees, living on sap or 
small animals. The eggs laid in these situations develop 
into grub-like larvae, which bore their way through living 
or dead wood, and in this condition sometimes live four or 
five years. They then transform into quiescent pupae (Fig. 
82), which finally burst their shells and emerge in the 
adult form. Others, like water-beetles and the whirligig- 
beetles, whose mazy motions are often seen on the surface 
of quiet streams, pass the larval period in the water. 
Under somewhat different conditions we find the potato- 
bugs, lady-bugs, fire-flies, and their innumerable relatives, 
but the changes they undergo in becoming adult are essen- 
tially the same as those described for the other members of 
the order. 

132. The moths and butterflies (Lepidoptera). — The moths 
and butterflies occur all over the world. In their mature 




Fig. 83.— Monarch-butterfly (Anosia plexippus). From photograph by A. L. Melan- 
der and C. T. Brues. 

state they are possessed of a grace of form and movement 
and a brilliancy of coloration that elicit our highest admi- 
ration. The mouth-parts are developed into a long pro- 
boscis, which may be unrolled and used to suck the nectar 
out of flowers, though in many of the adult moths, which 
never feed, it may remain unused. The wings, four in 
number, are covered with beautiful overlapping scales that 



142 



ANIMAL STUDIES 



adhere to our fingers when handled. This feature, and the 
general plan of the bod} 7 , which is much the same through- 
out the group, enables us to recognize most of them at once. 

___ __ : 




Fig. 84. — The silver-spot {Argynnis cybele). Photograph by A. L. Melaxder and 
C. T. Brum. 

133. The ants, bees, wasps, etc. (Hymenoptera). — The ants, 
bees, and wasps are the best-known insects belonging to 
this order. They are characterized by four membranous 
wings, by biting and sucking mouth-parts, and the female 
is often provided with a sting. All undergo a complete 
metamorphosis. The eggs may be laid in the bodies of 
other insects, or they may be placed in niarvelously con- 
structed homes, and be the objects of the greatest atten- 
tion, the parents or attendants often risking or losing their 
lives in their defense. The members of this order have 
long attracted attention, largely on account of their re- 
markable instinctive powers. They live in highly organized 
communities, and certain of their characteristics may be 
illustrated by a study of some of the more familiar forms. 



CHAPTEE XI 

ARTHROPODS {Continued). CLASS ARACHNIDA 

134. General characters. — In this group, comprising the 
spiders, mites, and a large assemblage of related species, we 
again meet with great differences in form and structure 
which fit them for lives under widely different conditions. 
The three regions of the body, head, thorax, and abdomen, 
so clearly marked in the insects, are here less plainly de- 
fined. The head and thorax are usually closely united, and 
in the mites the boundaries of the abdomen are also indis- 
tinct. The appendages of the head are two in number, and 
probably correspond to the antennae and mandibles of other 
Arthropods. In the scorpions and some species of mites 
these are furnished with pincers for holding the prey, and 
in other forms they act as piercing organs. Usually the 
thorax bears four pairs of legs, a characteristic which readily 
separates such animals from the insects. 

The internal organization differs almost as much as does 
the external. In many species it shows a considerable re- 
semblance to that of some insects, but in others, especially 
those of parasitic habits, it departs widely from such a type. 
Eespiration is affected by means of tracheae, or lung-books, 
which consist of sacs containing many blood-filled, leaf -like 
plates placed together like the leaves of a book. 

Usually, as in the insects, the young hatch from eggs 
which are laid, but in the scorpions and some of the mites 
the young develop within the body and at birth resemble 
the parent. Almost all of these organisms live either as 

143 



144 



ANIMAL STUDIES 



parasites or as active predaceous animals upon other animals. 
For this purpose many are provided with keen senses for 
detecting their prey and poisonous spines for despatching it. 
135. The scorpions. — Owing to the stout investing armor, 
the strong pincers, and the general form of the body, the 
scorpions might at first sight be mistaken for near relatives 

of the crayfish or lobster. 
A more careful examina- 
tion will show that the 
two pairs of pincers prob- 
ably correspond to the 
antennae and mandibles of 
the Crustacea that have 
become modified for seiz- 
ing the food. The swol- 
len part of the animal 
lying behind the four 
pairs of legs is a part of 
the abdomen, of which 
the slender " tail " consti- 
tutes the remainder. On 
the tip of the tail is a 
curved spine supplied 
with poison glands. Sev- 
eral pairs of eyes are borne 
on the dorsal surface of 
the head and thorax, while 
on the under side of the animal several slit-like openings 
lead into as many small cavities containing the lung-books. 
The scorpions are the inhabitants of warm countries, 
where they may be found under sticks and stones through- 
out the day. At night they leave their homes in search of 
food, which consists chiefly of insects anjd spiders. These 
are seized by means of the pincers, and the sting is driven 
into them with speedily fatal results. It is doubtful if the 
poison causes death in man, but the sting of some of the 




-Scorpion, showing pincer-like mouth- 
parts and spine-tipped tail. 



ARTHROPODS. GLASS ARACHN1DA 145 

larger species, which measure five or six inches in length, 
may produce certain disorders chiefly affecting the circula- 
tion. In this country there are upward of thirty species, 
most of which are comparatively small. 

136. The harvestmen. — The harvestmen or daddy-long- 
legs are small-bodied, long-legged creatures which resemble 
in general appearance several of the spiders. They differ 
from them, however, in the possession of claws correspond- 
ing to the smaller ones of the scorpion, and in their method 
of respiration, which is similar to that of insects. During 
the day they conceal themselves in dark crevices or stride 
slowly about in shaded places ; but at night they emerge 
into more open districts and capture small insects, from 
which they suck the juices. 

137. The spiders. — The spiders are world-wide in their 
distribution, and are a highly interesting group, owing 
chiefly to their peculiar habits. Examining any of our 
familiar species, it will be seen that the united head and 
thorax are separated by a narrow stalk from the usually 
distended abdomen. To the under side of the former are 
attached four pairs of long legs, a pair of feelers, and the 
powerful jaws supplied with poison-sacs, while eight shin- 
ing eyes are borne on the top of the head. On the abdo- 
men, behind the last pair of legs, are small openings into 
the lung cavities which contain a number of vascular, leaf- 
like projections known as lung-books. In some species 
a well-marked system of tracheae are also present. At the 
hinder end of the body are four or six little projections, 
the spinnerets, each of which is perforated with many 
holes. Through these the secretion, from the glands be- 
neath is squeezed out in the form of excessively delicate 
threads, often several hundred in number, which harden on 
exposure to the air. According to the use for which these 
are intended, they may remain a tangled mass or become 
united into one firm thread ; and according to the habits 
of the animal, they may be used for enclosing their eggs, 



146 



ANIMAL STUDIES 



for lining their burrows, or for the construction of webs of 
the most diverse patterns. 

138. The habits of spiders. — Many species of spiders, some 
of which are familiar objects in fields and houses, construct 
sheets of cobweb with a tube at one side in which they may 




Fig. 86.— A tarantula-spider (Eurypelma lentzii). Natural size. Photoyiaph by 
A. L. Melander and C. T. Brues. 

lie in wait for their prey or through which they may escape 
in times of danger. In the webs of the common orb- or 
wheel-weavers several radial lines are first constructed, and 
upon these the female spider spins a spiral web. Eesting 
in the center of this or at the margin, with her foot on 
some of the radial threads, she is able to detect the slight- 
est tremor and at once to rush upon the entangled captive. 
Some of the bird-spiders and their allies, living in trop- 
ical America, and attaining a length of two inches, con- 
struct web-lined burrows in the ground. From these they 
stalk their prey, which consists of various insects and even 



ARTHROPODS. CLASS ARACHNIDA 147 

small birds. These are almost instantly killed by the poison- 
fangs, and are then carried to the burrow, where the juices 
of the body are extracted. 

The trap-door spiders of the southwestern section of the 
United States also dig tunnels, which they cover with a 
closely fitting lid com- 
posed of earth. Eaising 
this they come out in 
search of insects, but if \U ; 'f'. 

sought in turn, they dash 
into the burrow, closing , .;' 
the door after them, and /, 

holding it with such firm- -'; •&'..' 
ness that it is rarely forced v ^ : . ;--i 4; 
open. If this should hap- > \L 
pen, there are sometimes " ; ' \m 
blind passage-ways, also in- 

closed with trap-doors, 
which usually baffle the 
pursuer. 

— ,. ,, ,, Fig. 87.— Trap-door spider and burrow 

Finally, there are (Cteniza). 

among the thousand spe- 
cies of spiders in the United States a considerable propor- 
tion which construct no definite web. Many of these may 
be seen darting about in the sunshine on old logs and 
fences, often trailing after them a thread which may sup- 
port them if they fall in their active leaping after in- 
sects. 

139. Breeding habits. — The male spiders are usually much 
smaller than the females, and some species are only one- 
fifteenth as long as the female and one one-hundredth of 
its weight. They are usually more brilliantly colored, more 
active in their movements, yet rarely spinning their own 
webs and capturing their own food, preferring to live at 
the expense of the female. At the breeding season the 
males of several species make a most interesting display 



14S 



ANIMAL STUDIES 



of their colors, activity, and gracefulness before the females ; 
and the latter, after watching these exhibitions, are said to 
select the one who has " shown off " in the most pleasing 
fashion. The life after this may be stormy, resulting in 
the death of the male ; but ordinarily the results are not 
so disastrous, and in a little while the female deposits her 
eggs in cases which she spins. In these the young develop, 
sometimes wintering here, and emerging in the spring to 
scamper about in search of food, or to drift through the 
air to more favorable spots on fluffy masses of cobweb. 

Few groups of animals are more interesting objects of 
study and more accessible. Their bites are rarely more 
serious than those of the mosquito — never fatal ; and a 
careful study of any species, however 
common, will undoubtedly bring to 
light many interesting and unknown 
facts. 

140. The mites and ticks. — The 
mites and ticks are the simplest and 
among the smallest of the animals 
belonging to this group. To the at- 
tentive observer they are rather com- 
mon objects, with homes in very dif- 
ferent situations. Some occur on liv- 
ing and decaying vegetation, in old 
flour and unrefined sugar, while oth- 
ers live in fresh water and a few in the sea. Almost all 
tend toward parasitism. Some of the insects which they 
pierce and destroy are a pest to man, but on the other hand 
some are intolerable owing to the diseases they produce. 

As to other parasitic organisms, degradation of structure 
is manifest. The respiratory system, so important to the 
active life of the insects, may be absent, the animal breath- 
ing through its skin. The circulatory system may be want- 
ing, the blood occupying spaces among the various organs 
being swept about by the animal's movements. And many 




Fig. 88.— The itch-mite (Sar- 
coptes scabei). 



ARTHROPODS. CLASS ARACHNIDA 



149 



other peculiarities have arisen which fit them for their 
different modes of life. 

141. The king crab (Limulus). — The king crab may be 
found crawling over the bottom or plowing its way through 
the sand and mud in many of the quiet bays from Maine 
to Florida. The large head and thorax of these animals 
are united into a horse- 
shoe-shaped piece, be- 
hind which lies the 
triangular abdomen. 
On the curved front 
surface of the former 
are a pair of small me- 
dian eyes, and farther 
outward are two larger 
compound ones. On 
the ventral side are 
six pairs of append- 
ages, instrumental in 
capturing and tearing 
the small animals that 
serve as food, and 
functioning in con- 
nection with the ter- 
minal spine as locomo- 
tor organs. On the 
ventral surface of the abdomen are numerous plate-like flaps 
which serve in respiration, and in the imperfect swimming 
movements in which these animals occasionally indulge. 

These relatively large and clumsy creatures are the rem- 
nant of a great number of strange, uncouth animals that in- 
habited the earth in past ages. Many of them show a close 
resemblance to the scorpions. The anatomy and develop- 
ment also show certain points of resemblance, and by some 
are thought to give us an idea of the ancient type of spider- 
like animal from which the modern forms have descended. 




-The king or horseshoe crab {Limulus 
polyphemus). 



CHAFTER XII 

ECHINODERMS 

142. General characters. — The division of the echino- 
derms includes the starfishes, sea-urchins, serpent- or brittle- 
stars, sea-cucumbers, and crinoids or sea-lilies. All are ma- 
rine forms, and constitute a conspicuous portion of the 
animals along almost any coast the world over. From 
these shallow-water situations they extend to the greatest 
depths of the ocean, and the bodily form possesses a great 
number of variations, adapting them to lives under such 
diverse conditions; and yet there is perhaps no group of 
organisms so clearly defined or exhibiting so close a resem- 
blance throughout. At one time it was thought that their 
radial symmetry was an indication of a close relationship 
to the coelenterates, but more careful study has shown them 
to be much more highly developed than this latter group, 
and widely separated from it. A skeleton is almost always 
present, consisting of a number of calcareous plates embed- 
ded in the body-wall, and often supporting numbers of pro- 
tective spines, which fact has given to the group the name 
Echinoderm, meaning hedgehog skin. 

143. External features.— The body of a starfish (Fig. 90) 
consists of a more or less clearly defined disk, from which 
the arms, usually five in number, radiate like the spokes 
of a wheel. At the center of the under side the mouth is 
located, and from it a deep groove, filled with a mass of 
tubular feet, extends to the tip of each arm. Innumerable 
calcareous plates firmly embedded in the body-wall serve 

150 



ECHINODERMS 



151 



for the protection of the internal organs, and at the same 
time admit of considerable movement. 

In the brittle-stars (Fig. 91) the central disk is much 
more sharply denned than in the preceding forms, and the 
long snake-like arms are capable of a very great freedom of 
movement, enabling the animal to glide over the sea-bottom, 
or through the crevices of the rocks, at a surprising rate. 

In several species, otherwise closely resembling those 




Fig. 90.— Starfish (Asterias ocracea), ventral view. One-half natural size. 

in Fig. 91, the arms divide repeatedly. These are the so= 
called basket-stars, living in the deeper waters of the sea, 
where they, like other brittle-stars, act as scavengers and 
devour large quantities of decomposing plant or animal 
remains. 

At first sight the globular spiny sea-urchins (Fig. 93) 
would scarcely be recognized as close relatives of the star- 
fishes. A closer examination, however, shows the mouth to 
be located on the under side of the body ; from it five rows 
of feet radiate and terminate close to the center of the 
dorsal side, and the arrangement of the plates forming the 



152 



ANIMAL STUDIES 



skeleton indicate that the sea-urchin is comparable to a 
starfish, with its dorsal surface reduced to insignificant 
proportions. 

In the sea-urchins the calcareous plates possess a great 
regularity, and are so closely interlocked that they prevent 




Fig. 91.— Brittle- or serpent-stars (species undetermined). Natural size. 

any motion of the body-wall. Also, each plate is usually 
provided with highly developed spines, movable upon a ball- 
and-socket joint. These spines serve for locomotion, and, 
in some instances, for conveying food to the mouth. A 
considerable number of sea-urchins show an irregularity in 
form which destroys to a corresponding degree the radial 
symmetry. This is due to various causes, but especially to 
a compression of the body, which, in the " sand-dollars,'' 



ECHINODERMS 153 

has resulted in the production of a thin, cake-like form 
(Fig. 94). 

If the spherical body of a sea-urchin were to be stretched 
in the direction of a line joining the mouth and the center 




Fig. 92.— Basket-star (Astrophytori). One-half natural size. 

of the dorsal surface, a form resembling a sea-cucumber 
(Fig. 95) would be the result. These latter organisms live 
among creyices of the rocks, embedded in the mud or bur- 
rowing in the sand at the bottom of the sea. In such situa- 
tions they are well protected, and a highly developed skele- 
ton, such as that of the sea-urchin, would not only be of 
little value, but a j)ositive hindrance to locomotion. The 
skeleton, therefore, is much reduced, consisting of a few 
scattered calcareous plates embedded in the fleshy body- 
wall. Another peculiar feature is almost universally pres- 
ent, in the form of a circlet of tentacles surrounding the 
mouth, which serve either for the purpose of respiration, 
for locomotion, or to convey food to the mouth. 

k very good imitation of the general plan of a sea-lily 
• or crinoid (Fig. 96) could be made by attaching a serpent- 



154 



ANIMAL STUDIES 



star, especially one of the basket-stars, by its dorsal side 
to a stalk. In the crinoids the numerous branches of the 

arms are compara- 
tively short, and in 
the arrangement of 
the internal organs 
there are numer- 
ous differences, but 
for iill that the re- 
semblance of these 
organisms tc the 
other echinoderms 
is undoubted. 

144. Haunts. — 
The greater num- 
ber of starfishes 
occur alongshore, 
slowly crawling 
about in search of 
food, or concealed 
in dark crevices of 
the rocks, where they may often be found as the tide goes 
out, and we know that in gradually lessening numbers other 
species lead similar lives at different levels far down in the 
dark and gloomy depths. In these same locations the sea- 
urchins occur, sometimes singly, but more usually associa- 
ted in great numbers, several species excavating hollows in 
the rocks, within which they obtain protection. The brit- 
tle-stars and sea-cucumbers may also be found occasionally 
in open view, but more often they make their way about in 
search of food buried in the sand. The crinoids are usual- 
ly inhabitants of deeper water, where they are found asso- 
ciated often in great numbers. A few species upon attain- 
ing the adult condition separate from the stalk, and are 
able to move about (Fig. 97), but the remaining species 
never shift their position. 




Fig. 93.— Sea-urchin (Strongylocentrotus purpuratus). 
Natural size. 



ECHINODERMS 155 

145. The organs of defense and repair of injury. — As we 

have seen, the body-wall of the echinoderms is provided 
with a series of plates, often bearing spines which serve as 
organs of defense, and to protect the internal organs. The 
starfishes and sea-urchins also possess numerous modified 
spines (pedicellaria) scattered over the surface of the body, 
which have the form of miniature birds' beaks, fastened to 
slender muscular threads. During life these jaws continu- 
ally open and close, and it is said they clean the body of 
debris that settles on it ; but on the other hand there are 
several reasons for the belief that they also act as organs 
of defense. Thus protected, the natural enemies of echino- 
derms appear to be relatively few, and are confined chiefly 
to some of the fishes whose teeth are especially modified 
for crushing them. In this 
way, and owing to the action 
of the breakers, they suffer 
frequent injury, but many 
species exhibit to a remark- 
able degree the ability to re- 
generate lost parts. Experi- 
ments show that if all the 
arms of a starfish be separa- 
ted from the disk the latter 
will within two or three 
months renew the arms ; and FlG - 94.-Sand-doiiar, a flat sea-urchin. 

" . _ Natural size. 

a single arm with a part 01 

the disk is able to renew the missing portions in about the 

same length of time. 

The brittle-stars, as their name indicates, are usually ex- 
cessively delicate, often dropping all of their arms upon the 
slightest provocation ; but here again the ability is present 
to develop the lost portions. 

Sea-cucumbers resent rough treatment by vigorously 
contracting their muscular walls and removing from the 
body almost the entire digestive tract, the respiratory tree, 




156 



ANIMAL STUDIES 



and a portion of the locomotor system ; but some species, at 
least, renew them again. In some of the starfishes and 
brittle-stars portions of the body 
appear to be voluntarily de- 
tached and to develop into new 
individuals, and it is thought 
that such self-mutilation is a 
normal method of reproduction. 
146. Locomotor system. — One 
of the most characteristic and 
remarkable features of the echi- 
noderms is the water-vascular 
system, a series of vessels con- 
taining water which serve in the 
process of locomotion. Their 
arrangement and mode of opera- 
tion are, with slight modifica- 
tions, the same throughout the 
group, and may be readily Un- 
derstood from their study in 
the starfish. 

On the dorsal surface of a 
starfish, in the angle between 
two of the arms, is a round, slightly elevated, calcareous 
plate, the madreporic body (Fig. 98, m.p.), which under 
the microscope appears full of holes, like the " rose " of a 
watering-pot. This connects with a tube that passes to 
the opposite side of the body, where it enters a canal 
completely encircling the mouth. On this ring-canal a 
number of sac-like reservoirs with muscular walls are at- 
tached, and from it a vessel extends along the under sur- 
face of each arm from base to tip. Each of these radial 
water-mains gives off numerous lateral branches that open 
out into small reservoirs similar to those located on 1^he 
ring-canal, and a short distance beyond communicate 
through the wall of the body with one of the numerous 




Fig. 95.— Sea-cucumber (Cucu- 
maria sp.). Natural size. 



ECHINODERMS 



157 



tube-feet, which, as we have seen, are slender tubular or- 
gans, many in number, filling the grooves on the ventral 
surface of each arm. This entire system of tubes and 
reservoirs is full of water, taken in, it is said, through the 
perforated plate, and, when the starfish wishes to advance, 
many of the little reservoirs con- 
tract, forcing water into the cav- 
ity of the feet, with which they 
are in communication, thus ex- 
tending the extremity of the tubes 
a considerable distance. The 
terminal sucker of each foot, act- 
ing upon the same principle as 
those on the cuttlefish, attaches 
firmly to some foreign object, 
whereupon the muscles of the 
foot contract, drawing the body 
toward the point of attachment. 
This latter movement , is similar 
to that of a boatman pulling him- 
self to land by means of a rope 
fastened to the shore. When the 
shortening of the tube-feet has 
ceased, the sucking disks release 
their attachment, project them- 
selves again, and this process is 
repeated over and over. At all 
times some of the feet are con- 
tracting, and a steady advance of 
the body is the result. 

This method of locomotion 
also obtains in the sea-urchins and cucumbers, but in the 
serpent-stars the tube-feet have become modified into feel- 
ers, and the animal moves, often rapidly, by means of twist- 
ing movements of the arms. The feet have this character 
also in the crinoids, where the animal is generally without 




Fig. 96.— Sea-iuy or crinoid. 



158 ANIMAL STUDIES 

the power of locomotion. In some of the sea-cucumbers 
five equidistant rows of tube-feet extend from one end of 
the body to the other, and the animal crawls worm-like 
upon any side that happens to be down ; but certain spe- 
cies living in the sand, 
where tube - feet will 
not work satisfactorily, 
have lost all traces of 
them, and creep like an 
earthworm from place 
to place. In all the 
sea-cucumbers the feet, 
situated nearthe mouth, 
have been curiously 
modified to form a cir- 







Fig. 97.— An unattached crinoid (Antedori). - 

half natural size. clet of tentacles, which 

range in form from 
highly branched to short and thick structures, and in func- 
tion from respiratory organs and those of touch to con- 
trivances for scooping up sand and conveying it to the 
mouth. 

147. Food and digestive system. — In the echinoderms the 
body-wall is comparatively thin (Fig. 98), and encloses a 
great space, the body-cavity, in which the digestive and re- 
productive organs are contained. As the former in various 
species is adapted for acting upon very different kinds of 
food, it shows many modifications ; but there are a few prin- 
cipal types which may be briefly considered. 

In the starfishes the mouth enters almost directly into 
the cardiac division of the stomach, a capacious, thin-walled 
sac, much folded and packed away in the disk and bases of 
the arms (Fig. 98, Z>). This in turn leads into the second 
pyloric portion (a), with thicker walls and dorsal, to the 
first, from which a short intestine leads to the exterior, 
near the center of the disk. Another conspicuous and im- 
portant feature is the so-called liver, consisting of a pair 



ECHINODERMS 



159 



of closely branched, fluffy glands (Z), extending the entire 
length of each arm and opening into the pyloric stomach. 

The starfishes are carnivorous and highly voracious, de- 
vouring large numbers of barnacles and mollusks which hap- 
pen in their path. If these are small and free they are 
taken directly into the stomach, but when one of relatively 
large size is encountered the starfish settles down upon it, 
and, slowly pushing the cardiac stomach through the mouth, 
envelops it in the folds. Digestive fluids are now poured 
over it, and the victim is speedily despatched and in a partly 
digested condition is gradually absorbed into the body, leav- 




Fig. 98. —Dissection of starfish to show : a, pyloric stomach ; b, bile-ducts (above), 
cardiac stomach (below) ; b.c, body-cavity ; /, feet ; g, spines ; i, intestine ; 
I, liver; m, mouth; m.p., madreporic plate; r, reservoir; r.c, ring canal; 
r.m., stomach retractor muscle ; r.v., radial vessel ; s, stone canal ; t, respira- 
tory tree. 

ing the shell and other indigestible matters upon the exte- 
rior. Oysters and clams close their shells when thus attacked, 
but a steady, continuous pull on the part of the starfish 
finally opens them, and the stomach is spread over the fleshy 
portions with speedily fatal results. In the interior of the 
body the food is transferred to the pyloric stomach, sub- 
jected to the action of the liver, and when completely dis- 
solved is borne to all parts of the body. 



160 ANIMAL STUDIES 

The digestive system of the starfishes, with its various 
subdivisions and appendages, is in some respects more com- 
plicated than in the other classes. This is most strikingly 
the case with the serpent-stars, where the entire system for 
disposing of the minute animals and plants on which it 
feeds consists of a simple sac communicating with the 
exterior by a single opening — the mouth. 

In the sea-cucumbers large quantities of sand are taken 
into the body, and the minute organisms and organic mat- 
ter are digested from it. In the sea-urchins the mouth is 
provided with five teeth, and the food consists of minute 
bits of seaweeds, which these snip off. Such diets evidently 
require a comparatively simple digestive apparatus, for in 
both it consists throughout its whole extent of a tube of 
equal caliber, in which the various divisions of esophagus, 
stomach, and intestine are little, if at all, defined. This 
is usually somewhat longer than the body, and therefore 
thrown into several loops ; and in the sea-cucumbers its last 
division is expanded and furnished with more highly mus- 
cular walls, which aid in respiration. 

148. Development. — With but a few exceptions, the eggs 
of the echinoderms are laid directly in the surrounding 
water, and for many days the exceedingly minute young 
are borne great distances in the tidal currents. During 
this period they show no resemblance to their parents, and 
only after undergoing remarkable transformations do they 
assume their permanent features. In every case they have 
a five-rayed form in early youth, but in several species of 
starfishes additional arms develop until there may be as 
many as twenty or thirty. 



CHAPTER XIII 

THE CHORDATES 

149. General characters. — Up to the present time we have 
been studying the representatives of a vast assemblage of 
animals whose skeletons, if they have any at all, are located 
on the outside of the body. In the corals, the mighty com- 
pany of arthropods, and the echinoderms, it is external. On 
the other hand, we shall find that the animals we are now 
about to consider, the fishes, frogs, lizards, birds, and mam- 
mals, are in possession of an internal skeleton. In some of 
the simpler fishes and in a number of more lowly forms (Fig. 
99) it is exceedingly simple, and consists merely of a gristle- 
like rod, the notochord (Fig. 101, nc) 9 extending the length 
of the body and serving to support the nervous system, which 
is always dorsal. This is also the type of skeleton found in 
the young of the remaining higher animals, but as they grow 
older the notochord gives way to a more highly developed 
cartilaginous or bony, jointed skeleton, the vertebral column. 

In the young of all these back-boned or chordate ani- 
mals, the sides of the throat are invariably perforated to 
form a number of gill-slits. In the lower forms these per- 
sist and serve as respiratory organs, but in the higher ani- 
mals they disappear in the adult. The chordates are thus 
seen to be distinguished by the possession of a dorsal nerv- 
ous cord supported by an internal skeleton and by the 
presence of gill-slits, characters which separate them widely 
from all invertebrates. 

The chordates may be divided into ten classes, seven of 

161 



162 



ANIMAL STUDIES 



which (the lancelets, lampreys, fishes, amphibians, reptiles, 
birds, and mammals) are true vertebrates, while the others 
embrace several peculiar animals of much simpler organiza- 
tion. 

150. The ascidians. — Among the latter are a number of 
remarkable species belonging to the class of ascidians or 

sea-squirts (Fig. 99). 
These are abundantly 
represented along our 
coasts, and are readily 
distinguished by their 
sac -like bodies, which 
are often attached at 
one end to shells or 
rocks. On the opposite 
extremity two openings 
exist, through which a 
constant stream of water 
passes, bearing minute 
organisms serving as 
food. "When disturbed 
they frequently expel 
the water from these 
pores with considerable 
force, whence the name 
" sea-squirt." While 
many lead solitary lives, 
numerous individuals of other species are often closely 
packed together in a jelly-like pad attached to the rocks, 
and others not distantly related are fitted to float on the 
surface of the sea. 

The young when hatched resemble small tadpoles both in 
their shape and in the arrangement of some of the more 
important systems of organs. For a few hours each swims 
about, then selecting a suitable spot settles down and ad- 
heres for life. From this point on degeneration ensues. 




-Ascidian or sea-squirt. 



THE CHORD ATES 163 

The tail disappears, and with it the notochord and the 
greater part of the nervous system. The sense-organs van- 
ish, the pharynx becomes remodeled, and numerous other 
changes occur, leaving the animal in its adult condition, 
with little in its motionless, sac-like body to remind one of 
a vertebrate. 

151. The vertebrates. — Since the remainder of this vol- 
ume is concerned with the vertebrates it will be well at the 
outset to gain some knowledge of their more important 
characteristics. One of the most apparent is the presence 
of a jointed vertebral column, composed of cartilage or 
bone, which supports the nervous system. To it are also 
usually attached several pairs of ribs, two pairs of limbs, 
either fins, legs, or wings, and in front it terminates in a 
more or less highly developed skull. In the space par- 
tially enclosed by the ribs, the body-cavity, a digestive sys- 
tem is located, which consists of the stomach and intestine, 
together with the attached liver and pancreas. The cir- 
culatory system is also highly organized, and consists of a 
muscular heart, arteries, and veins which ramify through- 
out the body. Breathing, in the aquatic animals, is car- 
ried on by means of gills, and in the air-breathing forms 
by means of lungs, which, like the gills, effect the removal 
of carbonic-acid gas and the absorption of oxygen. The 
nervous system, consisting of the brain situated in the 
head and the spinal cord extending through the body 
above the back-bone, even in the lower vertebrates, is far 
more complex than in the invertebrates. The sense-organs 
also attain to a high degree of acuteness, and in connec- 
tion with the highly organized nervous system enable these 
forms to lead far more varied and complex lives than in 
any of the animals heretofore considered. 



CHAPTER XIY 

THE FISHES 

152. General characters. — In a general way the name 
fish is applied to all vertebrates which spend the whole 
of their life in the water, which undergo no retrograde 
metamorphosis, and which do not develop fingers or toes. 
Of other aquatic chordates or vertebrates the ascidians un- 
dergo a retrograde metamorphosis, losing the notochord, and 
with it all semblance of fish-like form. The amphibians, 
on the other hand, develop jointed limbs with fingers and 
toes, instead of paired fins with fin rays. A further com- 
parison of the animals called fishes reveals very great dif- 
ferences among them — differences of such extent that they 
cannot be placed in a single class. At least three great 
groups or classes must be recognized: the Lancelets, the 
Lampreys, and the True Fishes. The general characters of 
all these groups will be better understood after the study 
of some typical fish, that is one possessing as many fish-like 
features as possible, unmodified by peculiar habits. Such an 
example is found in the bass, trout, or perch. In either fish 
the pointed head is united, without any external sign of a 
neck, to the smooth, spindle-shaped body, which is thus fitted 
for easy and rapid cleaving of the water when propelled by 
the waving of the powerful tail (Fig. 100). A keel also has 
been provided, enabling the fish to steer true to its course. 
This consists of folds of skin arising along the middle line of 
the body, supported by numerous bony spines or cartilaginous 
164 



THE FISHES 165 

rays. These are the unpaired fins, as distinguished from 
the paired ones, which correspond to the limbs of the higher 
vertebrates. In the bass or perch the latter are of much 
service in swimming, and are also most important organs in 
directing the course of the fish upward or downward, or for 




Pig. 100.— Yellow perch {Perca flaxescens). df, dorsal fins ; pc, pectoral fin ; v, ven- 
tral fin ; a, anal fin ; c, caudal fin. 

aiding the tail in changing the course from side to side ; 
or they may be used to support the animal as it rests upon 
the bottom in wait for food ; and, finally, they may serve to 
keep the body suspended at a definite point. 

In addition to an internal skeleton the bass or perch, 
like the greater number of fishes, is more or less enclosed 
and protected by an external one, consisting of a beautifully 
arranged series of overlapping scales, which afford protec- 
tion to the underlying organs, and at the same time admit 
of great freedom of movement. These usually consist of a 
horny substance, to which lime is sometimes added, and 
are peculiar modifications of the skin, something like the 
feathers, nails, and hoofs of higher forms. 

153. The air-bladder. — Naturally a fish's body is heavier 
than the water in which it lives, and there are reasons for 
thinking that the air-bladder (Fig. 106, a.U.) acts in the 



166 ANIMAL STUDIES 

bass and perch and many other fishes as a float to enable 
them, without much effort, to remain suspended at a defi- 
nite level. By compressing this sac, partly by its own mus- 
cles and partly by those of the body-wall, the bulk of the 
fish is made less, and it sinks ; upon the relaxation of these 
same muscles the body expands and rises again. Deep-sea 
fishes, when brought to the surface, where the pressure is 
relatively slight, are found with their air-bladders so dis- 
tended that they can not sink again, and the float of surface 
fishes would be as useless if they were to be carried into the 
depths below, so that such fishes are compelled to keep 
within tolerably definite limits of depth. Morphologically 
considered, the air-bladder is a modified or degenerate lung, 
and in many fishes it is lost altogether. 

154. Respiration. — Looking down the throat of the perch, 
or any other fish, a series of slits (the gill-openings), usually 
four or five in number, may be seen on each side communi- 
cating with the exterior. In the sharks these outer open- 
ings are readily seen, but in the bony fishes they open into 
a chamber on each side of the head, covered by a bony plate 
or gill-cover that is open behind. On raising these flaps 
the gills may be seen composed of great numbers of bright- 
red filaments attached to the bars between each slit. Dur- 
ing life the fish may be seen to open its mouth at regular 
intervals, and, after gulping in a quantity of water, to close 
it again, contracting the sides of the throat to force it out 
of the gill-openings and over the gill-filaments to the exte- 
rior. During this process the blood traversing the excess- 
ively thin filaments extracts the oxygen from the water and 
carries it to other parts of the body. 

With this information, let us return to the study of the 
three classes of fishes. 

155. The lancelet (Branchiostoma). — The lancelet, some- 
times called amphioxus (Fig. 101), the type of the class Lepto- 
cardii, is a little creature, half an inch to four inches long, in 
the different species, transparent and colorless, living chiefly 



THE FISHES 



167 



in sand in warm seas, the ten species being found in as 
many different regions. A lancelet may be regarded as 
a vertebrate reduced to its lowest terms. Instead of a 
jointed back-bone, it has a cartilaginous notochord, running 
from the head to the tail. A nervous cord lies above it, 
enclosed in a membranous sheath. Xo skull is present, and 
the nerve-cord does not swell into a brain. There are no 
eyes and no scales. The mouth is a vertical slit, without 
jaws. There is no trace of the shoulder-girdle (shoulder- 
blade and collar-bone) or pelvis (hip-bone) from which 




Fig. 101.— The California lancelet (Branchiostoma californiense). Twice the natural 
size, g, gills ; I, liver ; m, mouth ; n, nerve-cord ; nc, notochord. 

spring the paired fins, which, in true fishes, correspond to 
arms and legs. The circulatory system is fish-like, but there 
is no heart, the blood being driven about by the contraction 
of the walls of the vessels. Along the edge of the back and 
tail is a rudimentary fin, made of fin-rays connected by mem- 
brane. In the character and arrangement of its organs the 
lancelet is certainly like a fish, but in degree of develop- 
ment it differs more from the lowest fish than the fish does 
from a mammal. 

156. Lampreys (or Cyclostomes). — The class of lampreys 
stands next in development (Fig. 102). The notochord gives 
way anteriorly to a cartilaginous skull, in which is con- 
tained the brain, of the ordinary fish type. There are eyes, 
and the heart is developed, and consists of an auricle and 
a ventricle. As distinguished from the true fish, the lam- 
preys show no trace whatever of limbs or of the bones 
which would support them. The lower jaw is wholly want- 
ing, the mouth being a roundish sucking disk. The fins 



168 



ANIMAL STUDIES 



are better developed, but of the same structure as in the 
lancelet. There is no bony matter in the skeleton, and 
there are no scales. The nasal opening is single on the top 
of the front of the head. 

There are about twenty-five species in this class. Some 
of them, called lampreys, ascend the streams from the sea 




Fig. 102.— Lampreys. 

in the spring for the purpose of spawning. The young 
undergo a metamorphosis, at first being blind and tooth- 
less. The adults feed mostly on the blood of fishes, which 
they suck after scraping a hole in the flesh with their rasp- 
like teeth. The others, called hag-fishes, live in the sea 
and bore into the bodies of other fishes, whose muscles they 
devour. All are slender, smooth, and eel-shaped. 

From their structure and development we suppose that 
these eel-like forms existed long ago, probably before the 
more highly developed sharks and bony fishes made their 
appearance, but it is difficult to determine whether their 
simple organization is of such long standing or is not 
in part the result of semiparasitic habits, or a life spent 



THE FISHES 



169 



largely in burrowing. Like the lancelet and other simple 
chordates, they are of the greatest interest to the zoologist 
who gains from them some idea of the lowly vertebrate 
forms that peopled the earth long ago. 

157. True fishes. — The third class, Pisces or true fishes, 
to which the shark as well as the bass and perch belong, has 
a well-developed skeleton, skull, and brain. The lower jaw 
is developed, forming a distinct mouth, and there is at least 
a shoulder-girdle and pelvis ; although the fins these should 
bear are not always developed, the general traits are those we 
associate with the fish. Of the true fishes, there are again sev- 
eral strongly marked groups, usually called sub-classes, two 
of them wholly extinct. Of these, three chiefly interest us. 

158. The sharks and skates. — Very early in the life of 
the sharks (Fig. 103) and skates (Selachii or Elasmobrancliii) 




Fig. 103. — Soup-fin shark {Galeus zyopterus) from Monterey, Cal. 

a notochord appears, similar to that in the lancelet and the 
lampreys. As growth proceeds its sheath becomes broken 
up into a series of cartilaginous rings, which thus appear 
like spools strung on a cord. As the fish grows older these 
" spools " or vertebrae grow solid, cutting the notochord into 
little disks, and great flexibility is thus secured. Cartilagi- 
nous appendages also grow up and cover the spinal nerve- 
cord lying above, and give strength to the unpaired fins ; 
the paired fins also have their supports. The shoulder- 
12 



170 ANIMAL STUDIES 

girdle is placed behind the skull, leaving room for a distinct 
neck ; strong bars of cartilage bear the gills ; others form jaws 
to carry the teeth ; and a complex skull protects the brain 
and sense-organs, which are of a relatively high state of devel- 
opment. Throughout life the skeleton is of cartilage, with 
perhaps here and there a little bone where greater strength 
is required. Besides these, there are numerous minor 
characters which the student will readily find for himself. 

The sharks and skates or rays live chiefly in the sea, 
and some reach an enormous size, the largest of all fishes. 
Some are very ferocious and voracious ; others are very mild 
and weak, and the development of teeth is in direct pro- 
portion to their voracity of habit. In earlier geologic times 
there were many more species of them than now exist. 

159. The lung-fishes. — The lung-fishes (Dipnoi) are pe- 
culiar forms living in some of the rivers of Australia and 
the tropical regions of Africa and South America. In these 
the air-bladder is developed as a perfect lung. During the 
wet season they breathe like other fishes by means of gills, 
but as the rivers dry up they burrow into the wet mud and 
breathe by means of lungs which are spongy sacs of which 
the air-bladder of other fishes is a degenerate representative. 
As we shall see, they resemble in this respect the tadpoles 
and some adult Amphibia (frogs and salamanders). The 
paired fins are also peculiar in structure, having an elongate 
jointed axis, with a fringe of rays along its length, a struc- 
ture almost as much like that of the limbs of a frog as that 
of a fish's fin. In fact the Dipnoi must be regarded as an 
ancestral type, an ally of the generalized form from which 
Amphibia and bony fishes have descended. Only four liv- 
ing species of dipnoans are known, but great numbers of 
fossil species are found in the rocks. 

160. The bony fishes (Teleostei).— The bony fishes, or 
Teleosts, are distinguished by the bony skeleton, the sym- 
metrical tail, and by the development of the air-bladder as 
a more or less completely closed sac, useless in respiration. 



THE FISHES 171 

Often this organ is altogether wanting, as in the common 
mackerel. About twelve thousand kinds of bony fishes are 
known. The species swarm in every sea, lake, or river 
throughout the earth, and some form, or another among 
them is familiar to every boy in the land. These fishes are 
divided into about two hundred families, and these may be 
arranged in fifteen to twenty orders. As these are mostly 
distinguished by features of the skeleton, we need not name 
them here. In Jordan and Evermann's Fishes of North 
and Middle America, as well as in various other books, the 
student of fishes can find the characters by which orders 
may be distinguished. 

161. Sturgeons and garpikes (Ganoidei). — While the great 
majority of the typical fishes possess a bony skeleton, there 
are a few quaint types — the ganoid fishes showing ancient 
traits. In some of these, as the sturgeon, the sktleton is 
cartilaginous. In the garpike and bowfin it is long, as in 
the teleosts. Most of this group are now extinct. At 
present in this country the ganoids are represented by sev- 
eral species, the best known being the sturgeons. These in- 
habit the Great Lakes, the Mississippi, and its tributaries ; 
while other species ascend the rivers to spawn. These are 
the largest fishes found in fresh water, attaining a length 
of ten or twelve feet, and a weight of five hundred pounds. 
Their food consists of small plants and animals, which they 
suck in through their tube-like mouth. The garpikes live 
in the larger lakes and rivers throughout the East and 
Mississippi Valley. Their bodies, from three to ten feet in 
length, according to the species, are covered with compara- 
tively large regularly arranged square scales, and the upper 
jaw is elongated to form a kind of beak, abundantly sup- 
plied with teeth. They are carnivorous, voracious fishes, 
working great havoc among the more defenseless food- 
fishes. Equally destructive is the voracious bowfin (Amia), 
a fish useless as food, but of very great interest from its 
relation to extinct forms. 



172 ANIMAL STUDIES 

162. The catfishes. — Among the lowest bony fishes we 
may place the great group to which almost all fresh-water 
fishes belong. In this group the four vertebrae situated next 
the head are firmly united, and by means of certain small 
lever-like bones a connection is formed between the air-blad- 
der and the ear of the fish, which is sunk deep in the skull. 
The air-bladder thus becomes a sounding organ in the 
function of hearing. The family of catfishes possesses this 
structure, and the student should look for it in the first one 
he catches. The catfishes are remarkable for the long feel- 
ers about the mouth, with which they pick their way on the 
bottom of a pond. There are many kinds the world over. 
The small ones are known as horned pout or bullhead. In 
these the dorsal and pectoral fins are armed each with a 
strong, sharp spine, which is set stiff when the fish is dis- 
turbed, and makes them very troublesome to handle. The 
catfishes have no scales. 

163. The carp-like fishes. — The still greater carp family 
includes all the carp, dace, minnows, and chubs. They 
have the air-bladder joined to the ear, just like the catfish, 
but they lack the long feelers and the fin spines, while the 
soft body is covered with scales, and there are no teeth in 
the mouth. In the throat are a few very large teeth, which 
the ingenious boy should find. In the sucker family these 
throat teeth are like the teeth of a comb, and the mouth is 
fitted for sucking small objects on the river bottom. 

164. The eels. — In the great order of eels the body is 
long and slim, scaleless, or nearly so, with no ventral fins. 
The shoulder-girdle has slipped back from the head, so as 
to leave a distinct neck, while ordinary fishes have none. 
Of eels there are very many kinds — some large and fierce, 
some small as an earthworm ; and ons kind comes into fresh 
water. 

165. Herring and salmon. — In the great order which in- 
cludes the herring and salmon the vertebrae are all alike, 
the ventral fins far from the head, and the scales smooth to 



THE FISHES 



173 



the touch. The herring and shad are examples, as also the 
salmon and trout. Some live in the great depths of the 
sea, even five miles below the surface. These are very soft 
in body, being nnder tremendous pressure. They are inky 
black — for the sea at that depth seems black as ink — and 
most of them have luminous spots which give them light 
in the darkness. Some species have the forehead luminous, 
like the headlight of an engine. Most of these deep-sea 
fishes are very voracious, for there is nothing for them to 
feed on save their neighbors. 

166. The pike, sticklebacks, etc. — Several small orders 
stand between these soft-rayed, smooth-scaled fishes and 




C W 

Fig. 104— The blindfish and its parentage. A, Dismal Swamp fish (Chologaster 
avitns), the ancestor of (B) Agassiz's cave fish {Chologaster agassizi) and (C) 
cave blindfish ( Typhlichthys subterraneus). 



the form, like the perch and bass, which has many spines in 
the dorsal fin. Among these transitional forms is the pike 
(Fig. 105) —long, slender, circumspect, and voracious, lying 
in wait under a lily-pad; the blindfish, which lost its eyes 
through long living in the streams of the great caves ; the 
stickleback, small, wiry, malicious, and destructive, steal- 
ing the eggs and nibbling the fins of any larger fish ; 
the sea-horse, often clinging with its tail to floating 



THE FISHES 175 

seaweed, the male carrying the eggs about in his pocket 
until they hatch ; the mullet, stupid, blundering, feeding 
on minute plants, crushing them in a gizzard like that of 
a hen, but withal having soft flesh, good for the table ; the 
flying-fishes, which sail through the air with great swiftness 
to escape their enemies. 

167. The spiny-rayed fishes. — In the group of spiny- 
rayed fishes the ventral fins are brought forward and joined 
to the shoulder-girdle. The scales are generally rough to 
the touch, and the head is usually roughened also. There 
are many in every sea, ranging in size from the Everglade 
perch of Florida, an inch long, to the swordfish, which is 
thirty. These are the most specialized, the most fish-like 
of all the fishes. Leading families are the perch, in the 
fresh waters, the common yellow perch, familiar to all boys 
in the Xortheastern States ; the darters, which are dwarf 
perches, beautifully colored and gracefully formed, living 
on the bottoms of swift rivers ; the sunfishes, with broad 
bodies and shining scales, thriving and nest-building in 
the quiet eddies ; the sea-bass of many kinds, all valued for 
the table; the mackerel tribe, mostly swimming in great 
schools from shore to shore. After these come the multi- 
tude of snappers, grunts, weakfishes, bluefishes, rose-fishes, 
valued as food. Then follow the gurnards, with bony 
heads; the sculpins, with heads armed with thorns, the 
small ones in the rivers most destructive to the eggs of 
trout ; and at the end of the long series a few families in 
which the spines once developed are lost again, and the 
fins have only soft and jointed rays. It is a curious law of 
development that when a structure is once highly special- 
ized it may lose its usefulness, at which point degeneration 
at once sets in. Among fishes of this type are the cod- 
fishes, with spindle-shaped bodies, and the flounders, with 
flat bodies. The flounders lie on the sand with one side 
' down, and the head is so twisted that the eyes come out to- 
gether on the side that lies uppermost. This side is col- 



THE FISHES 177 

ored like the bottom — sand colored or brown or black — and 
the under side is white. When the flounder is first hatched, 
the eyes are on each side of the head, and the animal swims 
upright in the water like other fishes. But it soon rests on 
the bottom ; it turns to one side, and as the body is turned 
over the lower eye begins to move over to the other side. 
Finally, we may close the series with the anglers, in which 
the first dorsal spine is transformed into a sort of fishing- 
pole with a bait at the end, which may sometimes serve to 
lure the little fishes, which are soon swallowed when once 
in reach of the capacious mouth. 

168. Internal anatomy. — A few fishes are vegetarians, but 
the greater number are carnivorous. Some swallow large 
quantities of sand of the sea-bottom and absorb from it the 
small organisms living there. Others are provided with 
beaks for nipping off corals and tube-dwelling worms. Huge 
plate-like teeth enable others to crush mollusks, sea-urchins, 
and crabs, and many are adapted for preying upon other 
fishes. The latter are often able to escape, owing to the 
presence of numerous spines, sometimes supplied with 
poison-glands; or their colors are protective, and a vast 
number of devices are present which enable them with 
some degree of surety to escape their enemies and capture 
food. 

Usually, without mastication, the food passes into the 
digestive tract (Fig. 107), which in the main resembles that 
of the squirrel, but varies considerably according to the 
nature of the food it is required to absorb. As in other 
animals, it is usually longer in the vegetable feeders. In 
most fishes the walls of the canal are pushed out at the 
junction of the stomach and intestine, to form numerous 
processes like so many glove-fingers (the pyloric cosca, Fig. 
107, py-c), which probably serve to increase the absorptive 
surface. The same result is obtained in other ways, chiefly 
by numerous folds of the lining of the canal. 

The blood-system is much more complex in the fishes 



178 



ANIMAL STUDIES 



than in any of the invertebrates. It also differs in its gen- 
eral plan from that of most adult vertebrates, owing to the 
peculiar method of respiration. In almost every case the 
vessels returning from all parts of the body unite into one 
vein leading into the heart, which consists of only one 
auricle and ventricle (Fig. 107). From the heart the blood 




Fig. 107.— Dissection of a bony fish, the trout (Salmo). a.bl., air-bladder; an., anal 
opening; au., auricle ; gl.st., gills; gi/L, esophagus ; int., intestine ; kd.. kidney; 
lr., liver ; l.ov., ovary ; opt.L. brain ; py.c, pyloric coeca ; sp.c, spinal cord ; spl., 
spleen ; st., stomach ; v, ventricle. 

is forced through the gills, with all their delicate filaments, 
and now, laden with oxygen and nutritious substances, al- 
ready absorbed from the coats of the digestive tract, it 
travels on to all parts of the body, continually unloading 
its cargo in needy districts and waste matters in the kid- 
neys before returning once more to the heart. 

169. The senses of fishes. — The habits of fishes indicate 
that they know considerable of what is going on in the out- 
side world, and their well-developed sense-organs show the 
degree of their sensitiveness. A share of this information 
comes through the sense of touch, which is distributed all 
over the surface of the body, chiefly in the more exposed 
regions sometimes especially provided with fleshy feelers, 
like those on the chin of the catfish. 



THE FISHES 179 

The sense of smell appears to be fairly developed, as is 
that of hearing ; but there is no evidence of a sense of taste. 
A few fishes chew their food, and may possibly taste it, but 
there are others that swallow it whole, and in all there are 
relatively a few nerves going to the tongue or floor of the 
mouth. 

The eyes of most fishes are highly developed, and are of 
the greatest use at all times. Exceptions to the rule are 
found in certain species which live in caves or in the dark 
abysses of the ocean. In some of these the eyes have dis- 
appeared amost completely, and the sense of touch be- 
comes correspondingly more acute ; in other deep-sea forms 
they have grown to a large size, enabling them to distin- 
guish objects in the gloom, like the owls and other noc- 
turnal animals. Embedded in the skin of some of these 
deep-sea fishes, and certain nocturnal ones, are peculiar 
spots, composed of a glandular substance, which produces 
a bright glow like that of the fireflies. These may be located 
on the head or arranged in patterns over various parts of 
the body, and may serve to light the fish on its way and 
enable it to see its food to better advantage, or it may act 
as a lure to many fishes that become victims to their own 
curiosity. In those fishes which are active most of the 
time the eyes are located on the sides of the head, and in 
those which remain at or near the bottom they are turned 
toward the top ; in every case where they can be used to 
the best advantage. 

170. Breeding habits. — Among fishes the egg-laying time 
usually comes with the spring, when the males of several 
species become more resplendent, and sometimes engage in 
struggles for their respective mates. In others this cere- 
mony is performed without show of hostility. Some make 
nests, while others lay their eggs loosely in the water. 

In the salmon family, the eggs are laid in cooling waters, 
as in rivers or brooks. The young make their way down- 
ward, often entering the sea. When the young in the sea 



180 - ANIMAL STUDIES 

become mature they emigrate in great companies, and make 
their way hundreds, perhaps thousands, of miles to the 
rivers in which they spent their youth. Up these streams 
they rush in crowds, leaping over waterfalls and rapids, 
and, dashed and battered on the rocks, many, and in some 
species all, die from injuries or exhaustion after the breed- 
ing season is passed. The eggs, like those of the chubs, 
suckers, sunfishes, and catfishes, are usually buried in shal- 
low holes in the sand, and the males of most fishes keep a 
faithful watch over the young until they are able to live in 
safety. In some of the sticklebacks and in several marine 
species elaborate nests are composed of grass or seaweeds ; 
some of the catfishes carry the eggs until they hatch in 
their mouths or else in folds of spongy skin on the under 
side of the body ; in the pipefishes and sea-horses a slender 
sac along the lower surface of the male acts as a brood- 
pouch, in which the female places the eggs to remain until 
developed ; and some fishes, such as the surf-fishes and a 
number of the sharks, bring forth their young alive. On 
the other hand, the young of many of the herrings, salmon, 
cod, perch, and numerous other fishes are abandoned at 
their birth, and fall a prey to many animals, even the par- 
ents often devouring their own eggs. 

In the former cases, where the young are protected, only 
a relatively few eggs are produced : where they are aban- 
doned the female often lays many millions. In every case 
the number of eggs is in direct relation to the chances the 
young have of reaching maturity, a few out of each brood 
surviving to perpetuate the race. 

171. Development and past history.— The eggs of the 
higher bony fishes are usually small (one-tenth to one-third 
of an inch in diameter), and the young when they hatch 
are accordingly little ; in the sharks the eggs are larger, 
the size of a hen's egg or even larger, and the young when 
born are relatively large and powerful. These differences, 
however, do not greatly affect the early development, for 



THE FISHES 131 

in every case the head and then the trunk soon become 
formed, gills arise, the nervous system appears, which is 
invariably supported by a skeleton in the form of a gristly 
rod — the notochord. In the lower forms of fishes this per- 
sists throughout life ; but in the sharks and skates it be- 
comes replaced in the adult by another and higher type of 
skeleton, which is much more specialized with the bony 
fishes. 

Those who study the fossils on the rocks tell us that 
the first fishes were very simple, and many believe that 
their skeleton, like that of the little growing fish, consisted 
only of a notochord. Many of these old forms died out 
long ago, while others gradually changed in one way and 
another to adapt themselves to their surroundings, the con- 
stant need of adaptation having resulted in the multitude 
of present-day types. Some of the sharks have probably 
changed relatively only to a slight extent ; others, like the 
garpike, are much more altered ; and the bony fishes are 
far from their original estate, though their development 
has been rather toward a greater specialization for aquatic 
life than an advance upward. The little fish in its growth 
from the egg thus repeats the history of its ancestral 
development ; but as though in haste to reach the adult 
condition, it omits many important details. Moreover, the 
record in the rocks is not complete, and we have many 
things yet to learn of the ancient fishes and their develop- 
ment from age to age to the present day. 



CHAPTER XV 

THE AMPHIBIANS 

In many respects the amphibians — toads, frogs, and sala- 
manders — resemble the fishes, especially the lung-fishes 
(Dipnoi). The modern amphibians are essentially fishes 
in their early life, but in developing legs and otherwise 
changing their bodily form they become adapted for a life 
on land under conditions differing from those of the fishes. 
Judging from this class of facts, we may assume that fish- 
like ancestors, by the development of the lungs, became 
fitted for a life on land, and that from these the amphib- 
ians of our times have been derived. 

172. Development. — The eggs of the Amphibia are laid 
during the spring months in fresh-water streams and ponds. 
They are globular, about as large as shot, and are embedded 
in a gelatinous envelope (Fig. 108). They are either de- 
posited singly or in clumps, or festooned in long strings over 
the water-weeds. During the next few days development 
proceeds rapidly under favorable conditions, resulting in an 
elongated body with simple head and tail. In this condition 
they are hatched as tadpoles. As yet they are blind and 
mouthless, but lips and horny jaws soon appear, along with 
highly developed eyes, ears, and nose. External fluffy gills 
arise on the sides of the head, and slits form in the walls of 
the throat, between which gills are attached, and over which 
folds of skin develop, as in the fishes. A fin-fold like that 
of the lancelet or lamprey appears on the tail. The brain 
and spinal cord, extending along the line of the back, are 
supported by a gristly notochord, and complete and com- 
1S2 



THE AMPHIBIANS 



183 



plex internal organs adapt the animal to a free-swimming 
existence for days to come. 

The tadpole is now, to all intents and purposes, a fish — 
a fact most clearly recognized in its form, method of loco- 




Fig. 108.— Metamorphosis of the toad.— Partly after Gage. 

motion, the arrangement of the gills, and the general plan 
of the circulatory system. 

173. Further growth. — In the course of the next few 
weeks hind limbs develop beneath the skin, through which 
they finally protrude. In the same manner, fore limbs arise 
at a later date. In position these organs are like the paired 
fins of fishes, but they are intended for crawling or leaping 
on land, and are modified in accordance with this need. As 
in the higher vertebrates, the limbs develop as arms and 
legs, with long fingers and toes, between which are stretched 
webs of skin, which serve in swimming. 



184 ANIMAL STUDIES 

In the meantime large internal changes are also taking 
place. The wall of the esophagus has gradually pouched 
out to form the lungs. They are richly supplied with blood- 
vessels, closely resembling in their general features the 
lungs of the lung-fishes. The animal now rises to the sur- 
face occasionally to gulp in air, and it also continues to 
breathe by means of gills. At this stage of its existence, 
therefore, the larva is amphibious (two-living), and we have 
the interesting example of an animal extracting oxygen 
from both the water and the air. The diet of the tadpole 
at this time changes from vegetable to animal substances, 
and horny teeth give way to the small teeth of the frog, 
and the digestive system undergoes an entire remodeling 
to adapt it to its new duties. The young amphibian — 
whether frog, toad, or salamander — is now a four-legged 
creature, with well-developed head and tail, with lungs and 
gills, though the latter are usually fast disappearing, and is 
rapidly assuming those characters which will fit it for a 
terrestrial or semiaquatic existence. 

174. The salamanders. — The changes which now ensue in 
such a larva in reaching the adult condition are relatively 
slight in the lower salamanders. The external gills often 
persist (Fig. Ill), the lungs are also functional, and the 
changes are largely those of increase of size. In the larger 
number of species the gills disappear more or less com- 
pletely (Fig. 109), such species often abandoning the water 
for homes in damp soil or under stones and logs, returning 
to it only when the time comes for their eggs to be laid. 
The limbs are always relatively weak, never supporting the 
body from the ground, but serving in a clumsy way to push 
it from place to place. In the aquatic forms the tail con- 
tinues to serve as a swimming organ. In some species the 
hind legs become rudimentary, or even entirely lacking. 
A still further modification occurs in a few burrowing spe- 
cies, which move by wrigglings of the body, and are with- 
out either pairs of legs. 



THE AMPHIBIANS 



185 



In geological times many of the salamanders were of 
great size, several feet in length, and some were enclosed 
in an armor consisting of bony plates. All now living have 
the skin naked, and with the exception of the giant species 
of Japan, three feet in length, and a few similar forms in 
America, the modern representatives are comparatively 




zmm&jM: 



Fig. 109.— Blunt-nosed salamander (Amblr/sfoma opacuni). Photograph by W. H. 
Fisher. 

feeble and measure their length by inches. Only a few, on 
account of their bright colors, are particularly attractive, 
while the others are usually shunned and considered re- 
pulsive, chiefly because of their supposed poisonous char- 
acter, though in reality few animals are more harmless. 

175. Tailless forms.— In the frogs and toads the meta- 
morphosis which the young undergo is almost as profound 
as that which takes place with the insects. The gills, to- 
gether with their blood-vessels, disappear completely. The 
tail, with its muscles, nerve-supply, and skeleton, is ab- 
sorbed. The cartilaginous notochord gives way to a jointed 
back-bone. A skull is developed ; numerous bones form in 
the limbs, affording an attachment for the powerful muscles 
which make the toad, and especially the frog, expert swim- 
13 



186 ANIMAL STUDIES 

mers and leapers, and thus equipped they hereafter lead a 
wholly terrestrial or semiaquatic life. 

176. Distribution and common forms. — All the Amphibia 
are dependent upon moisture. Almost all are hatched and 
developed in fresh water, and those which leave the water 
return to it during the breeding season. So we find repre- 
sentatives of the group all over the world having much the 
same range as the fresh- water fishes. The great majority 
of the salamanders are confined to the northern hemisphere, 
but the toads and frogs are almost universally distributed. 

Among the salamanders in this country only a relatively 
few species completely retain their external gills. This is 
the case with sirens and mud-puppies or water-dogs (Fig. 
Ill), which may occasionally be seen in the clear waters 
of our lakes and rivers crawling slowly about in search of 
food, and every now and then rising to the surface to gulp 
in air. The remainder lose their gills more or less com- 
pletely, and usually leave the water for damp haunts on 
land. One of the blunt-nosed salamanders, known as the 
tiger salamander (Ambly stoma tigrinum), is found in moist 
localities in most parts of the United States. Besides these 
are numerous small species, among them the newts (Die- 
myctylus), ranging widely over the United States, living 
under logs and stones and feeding upon the small insects 
and worms inhabiting such situations. In several species 
of salamanders the lungs disappear with age, and respira- 
tion is performed solely through the surface of the skin. 

The tailless amphibians are much more abundant and 
familiar objects than the salamanders, and from the open- 
ing of spring until late in the fall they are met with on 
every hand. With few exceptions the frogs live in or about 
ponds and marshes, in which they obtain protection in 
troublous times and from which they derive the store of 
worms and insects that serve as food. On the other hand, 
the tree-frogs, as their name indicates, usually abandon the 
water and repair to moist situations in trees and other vege- 



THE AMPHIBIANS 187 

tation. Their shrill, cricket-like calls are often heard in 
the summer. The fingers and toes are more or less dilated 
into disks at their tips, enabling them to climb with con- 
siderable facility; and they are further adapted to their 
surroundings on account of their protective colors. The 
toads undergo their metamorphosis while very small, and 
approach the water only at the breeding season. During 
the day they remain concealed in holes and crevices, but at 
the approach of evening come out in search of food. 

177. Means of defense. — The food of the members of this 
group consists chiefly of small fishes, insect larvae, snails, 
and little crustaceans, which are swallowed whole. On the 
other hand, many Amphibia prey on each other, while most 
of them are eagerly sought by birds and fishes. Some, as 
the toads, stalk their food only during the night-time or 
depend upon their agility to escape their enemies. Others 
are colored protectively, the markings, of the skin resem- 
bling the foliage of the earth upon which they rest, and in 
some species, as the tree-toads, this color-pattern changes 
as the animal shifts its position. A few species are most 
brilliantly colored with red, green, yellow, or combinations 
of these, in striking contrast to their surroundings. They 
have apparently few enemies, possibly because of an un- 
pleasant odor or taste, and it has been suggested that their 
gorgeous tints are danger-signals, warning their would-be 
captors from attempting a second time to devour them. At 
the same time it is well known that the somber-hued toads 
emit a milky secretion from the warty protuberance of 
their skin which is intensely bitter, irritating to delicate 
skin, and poisonous to several animals. 

178. Skeleton. — As in all vertebrates, the skeleton of the 
amphibian first arises as a cartilaginous rod, the notochord, 
which is afterward replaced by a jointed back-bone, to 
which the limbs are attached. The back-bone is anteriorly 
modified into a flat, usually complex, skull. In the sala- 
manders the number of vertebrae is sometimes very large, 



18S 



ANIMAL STUDIES 



and the body correspondingly long and snake-like ; but in 
other cases parts of the vertebrae are reduced in number, 
and the body is rather short and thick. In the frogs and 
toads this reduction reaches its culmination, for only nine 
distinct vertebrae are present, the tail vertebrae, correspond- 
ing to those of the salamanders, being represented by a 
rod-like bone, the urostyle, made of segments grown to- 
gether. 

179. Digestive and other systems.— In its main characters 
the digestive tract of the amphibian (Fig. 110) resembles 

apMddb - tt %kd ovd. 




Fig HO.-Dissection of toad (Bufo). an., anal opening; au., auricle; bl bladder- 
duo., duodenum ; Ing., lung ; lr., liver; pn., pancreas ; ret., rectum ; spl spleen- 
St., stomach ; v., ventricle. ^ ' 

that of the fishes and the squirrel. The mouth is usually 
large, and the teeth are very small, as in the frog or sala- 
mander, or are lacking completely, as in the common toad 
In many salamanders the tongue, like that of a fish, is fixed 
and incapable of movement. In most of the frogs and 
toads it is attached to the front of the mouth, leavino- its 
hinder portion free, and capable of being thrown over and 
outward for a considerable distance. In the throat region 
gill-clefts may persist, but they usually close as the lungs 
reach their development. The succeeding portions of the 
canal are comparatively straight in the elongated forms, or 



THE AMPHIBIANS 189 

more or less coiled in the shorter species. In some cases 
no well-marked stomach exists, but ordinarily the different 
portions, as they are shown in Fig. 110, are well denned. 

As noted above, the circulation in the tadpole is the 
same as in fishes, then lungs arise, and for a time respi- 
ration is effected both by gills and lungs, and the cir- 
culation resembles in its essential points that of the 
lung-fishes. This may continue throughout life, but more 
frequently the gills and their vessels disappear, and the 
circulation approaches that of the reptiles. In such forms 
the heart consists of two auricles and one ventricle. Into 
the left auricle pours the pure blood from the lungs ; into 
the right the impure blood from the body. To some 
extent these mix as they are forced into the general cir- 
culation by the single ventricle. The amount of oxygen 
carried is therefore smaller than in the higher air-breathers, 
the amount of energy is proportionately less, and hence it 
is that all are cold-blooded and of comparatively sluggish 
habits. 

In some species of salamanders the lungs may also dis- 
appear, and breathing is carried on by the skin, as it is to 
a certain extent in all amphibians. In the frogs and toads 
lungs are invariably present, and vocal organs are situated 
at the opening of the windpipe in the throat. These pro- 
duce the characteristic croaking and shrilling, which in 
many species are intensified through the agency of one or 
two large sacs communicating with the mouth-cavity. 

Although the brain is small in the amphibians, it is 
more complex in several respects than it is in fishes. 
The eyes are also usually well developed, but in some of 
the cave and burrowing salamanders they are concealed 
beneath the skin, and are rudimentary. The ear varies 
considerably in complexity in the different species, but in 
the possession of semicircular canals and labyrinth resem- 
bles that of the fishes. In the frogs and toads, as one may 
readily discover, the drum or tympanum is external, ap- 



190 ANIMAL STUDIES 

pearing as a smooth circular area behind the eye. Organs 
of touch, smell, and taste are likewise developed in varying 
degree of perfection, 

180. Breeding-habits.— While the great majority of am- 
phibians mate in the spring and deposit their eggs in the 
water, often to the accompaniments of croakings and pip- 
ings almost deafening in intensity, several species, for 
various reasons, have adopted different methods. Some of 
the salamanders bring forth young alive, and several species 
of toads and frogs are known in which the young are cared 
for by the parent until their metamorphosis is complete. 
In one of the European toads (Alytes) the male winds 
the strings of eggs about his body until the tadpoles are 



p 1 "- ' ' :' t 




!, M 


# Hi mfJBBBg 


W^~&r" ■**? ■ 


afj 


Fig. 111.— Salamanders. The 
axolotl (the larva of Am- 
blystoma tigrinum) and 
the newt {Diemyctylus to- - 
rosus). 







ready to hatch ; and in a few species of tree-toads the eggs 
are stored in a great pouch on the back of the parent until 
the early stages of growth are over. In the Surinam toad 
of South America the eggs are placed by the male on the 
back of the female, and each sinks into a cavity in the 
spongy skin. Here they pass through the tadpole stage 
without the usual attendant dangers, and emerge with the 
form of the adult. 



THE AMPHIBIANS 191 

Sunlight and warmth are apparent necessities for speedy 
development. Tadpoles kept in captivity where the con- 
ditions are generally unfavorable may require years to as- 
sume the adult form. As mentioned above, the tiger sala- 
mander (Amblystoma tigrinum) occurs in most parts of the 
United States and Mexico. In the East this species drops its 
gills in early life as other salamanders do, and assumes the 
adult form, but in the cold water of high mountain lakes, 
in Colorado and neighboring States, it may never become 
adult, always remaining as in Fig. 111. This peculiar form 
is locally known as axolotl. In this condition it breeds. It 
is thus one of the very few examples of animals whose un- 
developed larvae are able to produce their kind. Owing to 
this trait it was at first considered a distinct species, and 
many years elapsed before its relationship to the true adult 
form was discovered. 



CHAPTER XVI 

THE REPTILES 

181. General characteristics. — In all the reptiles the gen- 
eral shape of the body, and to some extent the internal 
plan, is not materially different from that seen among the 
amphibians. In spite of external resemblance the actual 
relationship is not very close. It appears to be true that 
ages ago the ancestors of the modern reptiles were aquatic 
animals, possibly somewhat similar to some of the sala- 
manders; but they have become greatly changed, and 
are now, strictly speaking, land animals. At no time in 
their development after leaving the egg do we find them 
living in the water and breathing by gills. Some species, 
such as the turtles, lead aquatic or semiaquatic lives, but 
the modifications which fit them for such an existence 
render them only slightly different from their land-inhabit- 
ing relatives. The skin bears overlapping scales or horny 
plates, united edge to edge, as in the turtles, enabling them 
to withstand the attacks of enemies and the effects of heat 
and dryness. Indeed, it is when heat is greatest that rep- 
tiles are most active. In no other class of vertebrates, and 
very few invertebrates, do normal activities of the body 
appear to be so directly dependent upon external warmth. 
In the presence of cold they rapidly grow sluggish, and 
sink into a dormant state. 

As in the case of all animals, habits depend upon 
structure, and accordingly among the reptiles we find 
many remarkable modifications, enabling them to lead 
192 



THE REPTILES 



193 



widely different lives. Nevertheless all are constructed 
upon much the same plan. 

182. The lizards (Sauria).— As in the amphibians, es- 
pecially the salamanders, the body (Fig. 112) consists of 
a relatively small head united by a neck to the trunk. 




Fig. 112.— Common lizard or swift (Sceloporus undulatus). Photograph by W. H. 
Fisher. 

which, in turn, passes insensibly into a tail, usually of con- 
siderable length. Two pairs of limbs are almost always 
present, and these exhibit the same skeletal structure as 
in the amphibians; but in their construction, as in the 
other divisions of the body, we note a grace of propor- 
tion and muscular development which enable the lizards 
to execute their movements with an almost lightning-like 
rapidity. The mouth is large and slit-like, well armed with 
teeth, and the eyes and ears are keen. Scales of various 



194 ANIMAL STUDIES 

forms and sizes, always of definite arrangement, cover the 
body. The scales are always colored, in some species as 
brilliantly as the feathers of birds, and usually harmonize 
with the surroundings of the animal, enabling it to escape 
the attacks of its many enemies. Altogether the lizards 
are a very attractive group of animals. As in the salaman- 
ders, the vertebral column is usually of considerable length, 
but it too presents a lighter appearance and a greater flexi- 
bility. Slender ribs are present, and a breast-bone and the 
girdles which support the limbs. Although more ossified 
than in the amphibians, the skull still continues to be com- 
posed here and there of cartilage. The roof also is yet 
incomplete, but with the firm plates on the surface of the 
head ample protection is afforded the small brain under- 
neath. As above mentioned, the limbs are slender and 
insufficient to support the body, which accordingly rests 
upon the ground, and by its wrigglings and the pushing of 
the limbs is borne from place to place. It will be recalled 
that some of the salamanders living in subterranean haunts 
and burrowing in the soil have no need of limbs, and the 
latter have accordingly disappeared. This condition is 
paralleled by certain species of lizards. The blindworms 
(which are neither blind nor worms, but true lizards, though 
snake-like in appearance) are devoid of limbs, as are also 
the " glass-snakes." In some species the hinder pair arise 
in early life, but they remain small, and ultimately disap- 
pear. In almost all lizards the tail is very brittle, breaking 
at a slight touch. In such case the lost member will grow 
again after a time. 

183. The snakes (Serpentes).— The snakes are character- 
ized by a cylindrical, generally greatly elongated body, in 
which the divisions into head, neck, trunk, and tail are not 
sharply defined. As we have seen, this is also true of cer- 
tain lizards, but the naturalist finds no difficulty in detecting 
the differences between them. Another peculiarity of the 
snakes is in the great freedom of movement of the bones 



THE REPTILES 



195 



not concerned with the protection of the brain. In the 
reptiles the lower jaw does not unite directly with the 
skull, as in the higher animals, but to an intermediate 
bone, the quadrate, which is attached to the skull. In the 
snakes these unions are made by means of elastic liga- 
ments. The two halves of the lower jaw are also held 




Fig. 113.— Blacksnake (Bascanion constrictor). Photograph by W. H. Fisheb. 

together by a similar band, so that the entire palate and 
lower jaw are loosely hung together. This enables the 
snake to distend its mouth and throat to an extraordinary 
degree, and to swallow frogs and toads but slightly smaller 
than itself. Where the prey is of relatively small size, the 
halves of the lower jaw alternate with each other in pulling 
backward, thus drawing the food down the throat. The 
food is never masticated. The teeth are usually small and 
recurved, and serve only to hold the food until it may be 
swallowed. The latter process is facilitated by the copious 
secretion of the salivary glands, which become very active 
at this time. 

A further character of the snakes is the absence exter- 



196 ANIMAL STUDIES 

nally of any trace of limbs. However, in some of the 
pythons and boas hind limbs are present in the form of 
small groups of bones embedded beneath the skin and ter- 
minating in a claw. There thus appears to be no doubt 
that the ancestors of the modern snakes were four-footed, 
lizard-like creatures, which have assumed the present form 
in response to the necessity of adaptation to new conditions. 

More than any other order of vertebrates do the snakes 
deserve the name of creeping things, and yet their method 
of locomotion enables them to crawl and swim with a ra- 
pidity equal to that of many of the more highly developed 
animals. This depends chiefly upon certain peculiarities 
of the skeleton, which consists merely of a skull, vertebral 
column, and ribs. The vertebrae, usually two or three hun- 
dred in number, are united together by ball-and-socket 
joints, and each attaches by similar joints a pair of slender 
ribs. These in turn are attached to the broad outer plates 
upon which the body rests, and the whole system is operated 
by a powerful set of muscles. Upon the contraction of the 
muscles the ventral plates are made to strike backward 
upon the ground or other rough surface, which drives the 
body forward. Also, the ribs may be made to move back- 
ward and forward, and the snake thus progresses like a 
centiped or " thousand-legs." 

184. The turtles (Chelonia). — In many respects the tur- 
tles are the most highly modified of all the reptiles. The 
body (Fig. 114) is short and wide and enclosed in a shell or 
heavy armor, consisting of an upper portion, the carapace, 
and a flat ventral plate, the plastron. The shape of the 
carapace varies greatly from a low, flat shield to a highly 
vaulted dome, remaining cartilaginous throughout life, as 
in the soft-shelled turtles, or becoming bony and of great 
strength. The two portions of the shell form a box-like 
armor through whose openings may be extended the head, 
tail, and limbs. As a means of protection the turtle may 
retract these organs within the shell. The head is generally 



THE REPTILES 



197 



thick-set and muscular, and provided with horny jaws 
entirely destitute of teeth, like those of the birds. The 
limbs also are usually short and thick and variously shaped, 
and adapted for aquatic or terrestrial locomotion. The 
number of vertebras in the body and tail are relatively few,' 
and the thick and heavy body is devoid of the elements of 
grace and agility of movement characteristic of the other 
reptiles. On the other hand, the former enjoy a freedom 
from the attacks of enemies not accorded to animals in 
general. 

At first sight the appearance of a turtle does not indi- 
cate a close relationship to the other reptiles, but a more 




Fig. 114.— Box -turtle (Terrapene Carolina). 

careful examination, and especially of their development, 
discloses a remarkable resemblance. The head, tail, and 
limbs are essentially similar to those of the lizards, but in 
the trunk region peculiar modifications have taken place. 
The ribs at first separate, as in other animals, flatten 
greatly, and unite with a number of bones embedded in 
the skin, thus forming one great plate overlying the back 
of the animal. About the circumference of the shield 
other dermal or skin-bones are added, which increase the 
area of the carapace, and at the same time still others have 



198 ANIMAL STUDIES 

arisen and united on the ventral surface to form the plas- 
tron. In this process the shoulder- and hip-girdles which 
attach the limbs come to be withdrawn into the body, and 
we have the curious example of an animal enclosed within 
its back-bone and ribs. This is even more the case with 
the box-turtles (Fig. 114), common in the eastern United 
States, whose ventral plate is hinged so that after the 
limbs, head, and tail have been withdrawn it may be made 
to act like a lid to completely enclose the fleshy parts of 
the body. 

Scales and horny plates are present, as in other reptiles, 
the former covering all parts of the body except the cara- 
pace and plastron, which support the plates. In nearly all 
species the latter are of considerable size, and in the tor- 
toise-shell turtles are valuable articles of commerce. They 
also are sculptured in a fashion characteristic of each spe- 
cies, and may, like the colors of other animals, render them 
more like their surroundings, and consequently incon- 
spicuous. 

185. Crocodiles and alligators (Crocodilia).— The alligators 
(Fig. 115) and crocodiles are much more complex in struc- 
ture than the lizards, though their general form is much the 
same. The body is covered with an armor of thick bony 
shields and horny scales. These, along the median line, are 
keeled, and extending along the length of the laterally com- 
pressed tail form an efficient swimming organ and rudder. 
The mouth is of large size, and is bounteously supplied with 
large conical teeth, which are set in sockets in the jaw, and 
not fused with it, as in many of the lizards. The nose and 
ears may be .closed by valves to prevent the entrance of 
water, and a similar structure blocks its passage beyond 
the throat while the mouth is open. When large animals, 
such as hogs or calves, are captured as they come to drink, 
these devices enable the alligator or crocodile to sink with 
them to the bottom and hold them until drowned. The 
limbs, short and powerful, are efficient organs of locomo- 



THE REPTILES 199 

tion on land, and together with the general shape of the 
body, are also well adapted for swimming. 




Fig. 115.— Alligator (Alligator mississippiensis). 

186. Distribution of the lizards. — In a general way the 
number of reptiles is greatest where the temperature is 
highest. The tropics therefore abound in species, often 
of large size, and usually of bright coloration. As one 
travels northward the numbers rapidly diminish, their size 
is smaller, and the tints less pronounced. In all probability 
not less than four thousand known reptiles exist, whose 
haunts are of the most varied description. 

In North America the lizards are almost exclusively 
confined to the southern portions, only a very few species 
extending up to the fortieth parallel. Among these the 
skinks (Fumeces) are most widely distributed. The blue- 
tailed skink is probably the most familiar, a small lizard 
eight or ten inches in length, dark green with yellowish 
streaks and a bright-blue tail. On sunny days it may 
sometimes be seen darting about on the bark of trees in 
search of insects, upon which it feeds. 

One of the most familiar lizards in this country is the 
"glass-snake," found burrowing in the drier soil of the 
southern half of the United States east of the Mississippi. 



200 



ANIMAL STUDIES 



Both pairs of limbs are absent, but by wriggling movements 
of the body this lizard is able to force its way through light 
soil with considerable rapidity. It is a matter of some 
difficulty to secure entire specimens, for with other than 
the gentlest handling the tail severs its connection with 
the body, as the vertebras in this portion are extremely 
brittle. This peculiarity, together with its shape, has given 
it the popular name of glass-snake. Many species of liz- 
ards will thus detach the tail, a habit which is a means of 
protection, enabling the animal to scamper away into a 
place of safety while its enemy is concerning itself with 
the detached member. Later on a new tail develops, 
though usually of a less symmetrical form. 

187. Horned toads.— The horned toads (Phrynosoma) are 
lizards peculiar to the hot, sandy deserts and plains of 




Fig. 116.— Gila monster {Heloderma suspectum). One-third natural size, 



Mexico and the western United States. The body is com- 
paratively broad and flat, almost toad-like, and is covered 
with scales and spines of brownish and dusky tint, so like 
dried sticks and cactus spines in form and color as to ren- 
der them difficult of detection. In captivity they readily 



THE REPTILES 201 

adapt themselves to their new surroundings, become tame, 
and feast on flies, ants, and other insects, which they cap- 
ture by the aid of their long tongue. The horned toads 
are perfectly harmless creatures, but when irritated some- 
times perform the remarkable feat of spurting a stream of 
blood from the eye toward the intruding object for a dis- 
tance of several inches. This has been regarded by some 
as a zoological fable ; but there are many who have watched 
the horned toad in its natural state and in captivity, and 
they assure us that it is a fact. 

In the hot deserts of Arizona and Sonora is another 
peculiar species of lizard known as the Gila monster (Helo- 
derma) (Fig. 116), having the distinction of being the only 
poisonous lizard known. Further protection is afforded 
by bony tubercles on the head and by scales over the 
remainder of the body, all of which are colored brown or 
various shades of yellow, giving the animal a peculiar 
streaked and blotched appearance. 

188. Distribution of the snakes. — The snakes are much 
more common than the lizards. All over the United States 
one meets with them, especially the garter- or water-snakes. 
Of less wide distribution are the black-, grass-, and milk- 
snakes, and a number of less known species, all of which 
are perfectly harmless and often make interesting pets. 
Some of them when cornered show considerable temper, 
flatten the head and hiss violently, and imitate poisonous 
forms, but venomous snakes are comparatively few in num- 
ber in northern and eastern United States. In the south- 
ern portions of the country they become more abundant. 
Along the streams and in the swamps the copperheads, and 
especially the water-moccasins, often lie in wait for frogs 
ind fish. Both these species are especially dreaded, as they 
strike without giving any warning sound, but the name 
a ad bad reputation of the moccasin is often, especially in 
the South, transferred to perfectly harmless water-snakes. 
On higher ground are the rattlesnakes (Crotalus), once 
14 



202 



ANIMAL STUDIES 



abundant but now in many regions well-nigh exterminated. 
In these species the tail terminates in a series of horny 




by w. h. 



rings that produce a buzzing sound like that of the locust 
when the tail is rapidly vibrated. 

189. Distribution of the turtles. — The turtles are perhaps 
somewhat less dependent upon warmth than other reptiles, 
yet they too delight to bask in the sunshine, and soon grow 
sluggish in its absence. In all our fresh-water streams and 
ponds they are familiar objects, and several species extend 
up into Canada. Among the turtles the soft shell, the 
painted and the snapping turtles have the widest distri- 
bution, scarcely a good-sized stream or pond from the Gulf 
of Mexico to Canada, and even farther north, being without 
one or more representatives. All are carnivorous and vora- 
cious, and the snapping turtles are especially ferocious, and 
" for their size are the strongest of reptiles." In the woods 
and meadows the wood-tortoise and box-turtles are occa- 



THE REPTILES 203 

sionally met with, and at sea several turtles exist, some of 
them of great size. Among these is the leather-turtle, 
found in the warmer waters of the Atlantic, lazily floating 
at the surface or actively engaged in capturing food. They 
attain a length of from six to eight feet, and a weight of 
over a thousand pounds, and are sometimes captured for 
food when they come ashore to "bury their eggs in the sand. 
By this same method the loggerheads, the hawkbills, and 
the common green turtles are also captured in consider- 
able numbers. These are of smaller size, and the second 
named is of considerable value, as the horny plates cover- 




Fig. 118.— Hawkbill turtle (Eretmochelys imbricata). 

ing the shell furnish the tortoise-shell of commerce. These 
plates are removed after the animal is killed, by soaking 
in warm water or by the application of heat. 

190. Food and digestive system. — Some reptiles, among 
which are a number of species of lizards and the box- and, 
green turtles, are vegetarians, but the great majority are 



204 



ANIMAL STUDIES 



carnivorous, and usually very voracious. The lizards espe- 
cially devour large quantities of insects and snails, together 
with small fishes and frogs. The latter figure largely in 
the turtle's bill of fare, and in that of the snakes, which 
also capture birds and mammals. On the other hand, many 
of the reptiles prey upon one another ; and they are the 
favorite food of hawks and owls and numerous water-birds, 
of skunks and weasels and many other animals, which look 
for them continually. Many of the turtles, owing to their 
protective armor, and the snakes because of their poison- 
ous bite or great size and strength, are more or less ex- 
empt, but this is not true of their eggs and young. The 
smaller species depend upon keenness of sense, agility, and 
inconspicuous tints. These latter may undergo changes 
according to the character of the surroundings, but usually 
only to a slight extent. The chameleons of the tropics 
and a similarly colored green lizard on the pine-trees in 
the Southern States are able to change with great rapidity 
from green, through various shades, to brown. 

191. Respiration and circulation. — While still in the egg 
the young lizard develops rudimentary gills, and thus bears 



nam 
extnax 
intm 



e^^%J^J^lmdMM kd. 




Fig. 119.— Dissection of lizard (Scelopoms). an., anal opening ; au.. auricle ; crb.h., 
brain ; coec, intestine ; kd., kidney ; Ling., left lung ; lr., liver ; pn., pancreas ; 
sp.c, spinal cord ; spl., spleen ; St., stomach ; v., ventricle of heart. 



evidence to the fact that its distant ancestors were aquatic ; 
but before hatching they disappear, and lungs arise, which 



THE REPTILES 205 

remain functional throughout life. Corresponding to the 
shape of the body, these are usually much elongated and 
ordinarily paired (Fig. 119, l.lng.). The snakes are peculiar 
in having the left lung rudimentary or even lacking com- 
pletely, while the right one becomes greatly elongated and 
extends far back into the body. In nearly all the reptiles 
the amount of oxygen brought into the lungs is relatively 
large and the activity of the animal is proportionately 
great. The circulation of reptiles shows an advance be- 
yond that of the Amphibia. As in the latter, there are 
two distinct auricles ; but the chief difference arises from 
the fact that the ventricle is more or less divided by a par- 
tition which to a considerable degree prevents the blood 
returning from the lungs from mixing with the impure 
blood as it returns from its journey over the body. In the 
crocodiles and alligators the partition is complete, and the 
circulation thus approaches close to that of the higher 
animals. 

192. Hibernation. — Attention has already been called to 
the fact that reptiles are very susceptible to cold, rapidly 
growing less active as the temperature lowers. "When win- 
ter comes on they seek protected spots, and either alone 
or grouped together hibernate. The various activities of 
the body during this period are at very low ebb. The blood 
barely circulates, breathing is imperceptible, and stiff 
and insensible to the world about them they remain until 
the warmth again stirs them to their former activity. 
Some of our common turtles must also pass a somewhat 
similar sleep while embedded far down in the mud during 
the disappearance of the ponds in summer. At such times 
no food is taken, but owing to their loss in weight it is 
probable that a slow consumption of the body supplies the 
small amount of necessary energy. 

193. Nervous system and sense-organs. — At first sight one 
is struck with the small size of the brain of fishes, Am- 
phibia, and reptiles. Their intelligence likewise is at low 



206 ANIMAL STUDIES 

ebb. Almost all the movements and operations of the body 
appear to be carried on by the animal with little apparent 
thought. Their acts, like most of the animals below them, 
are said to be instinctive ; yet they are sufficiently well done 
to enable the animal to procure its food, avoid its enemies, 
and lead a successful life. As is true of other animals, the 
ability of the reptile to cope with its surroundings depends 
to a great extent upon the keenness of one or all of its or- 
gans of special sense. In the reptiles the sense of sight is 
perhaps sharpest, but there Is considerable variation in this 
respect. Movable eyelids are present in most lizards, to- 
gether with a third, known as the nictitating membrane, a 
thin, transparent fold located at the inner angle of the eye, 
over which it is drawn with great rapidity. Snakes have 
no movable eyelids, hence the eye has a peculiar stare. 
Furthermore, their sense of sight, except in a few tree-dwell- 
ing species, appears to be defective, the majority depending 
largely upon the sense of touch. 

In all the vertebrates a very peculiar organ known 
as the pineal gland or eye is situated on the roof of the 
brain. In several lizards its position is indicated by a trans- 
parent area in one of the plates of the head, and by an 
opening in the bones of the roof of the skull. In young 
reptiles, and especially in one of the Xew Zealand lizards 
{Hatteria, Fig. 120), its resemblance to an eye is decidedly 
striking. Lens, retina, pigment, cornea, are all present 
much as they are in some of the snails, but they finally 
degenerate more or less as the animal reaches maturity. 
It is a general belief that it represents the remnant of an 
organ of sight, a third eye, which looked out through the 
roof of the skull in some of the ancient vertebrates. 

With the possible exception of the few species of reptiles 
which produce sounds, probably to attract their mate, the 
sense of hearing is not particularly well developed. The 
senses of smell and taste are also comparatively feeble. The 
latter sense is located in the tongue, which is also popularly 



THE REPTILES 207 

supposed to serve for the purpose of defense, and that it is 
in some way related to the poison-glands. This, however, 
is an error. The tongue is used primarily as an organ of 




Fig. 120.— Tuatera (Sphenoaou punctatus). 

touch, and in snakes especially it is almost continually 
darted in and out to determine the character of the animal's 
surroundings. 

1 94. Egg-laying.— The eggs of the reptiles are relatively 
large and enclosed in a shell like a bird's egg, the shell, 
however, being leathery rather than made of lime. These 
are deposited in some warm situation, and generally left to 
themselves to hatch. Under stones, logs, and leaves, or 
buried lightly in the soil, are the positions most frequently 
chosen by the lizards and snakes. The turtles almost 
invariably select the warm sand at the edge of the water, 
and after scooping a hole lay numerous spherical eggs, 
usually at night. The alligators lay upward of a hundred 
eggs about the size of those of a goose, and guard them 
jealously until and even after they hatch. On the other 
hand, the young of many lizards and snakes are born alive, 
the eggs being hatched within the body. 

Many reptiles are surprisingly slow in attaining maturity, 
and live to an age attained by few other animals. It is a 
well-known fact that turtles live fully a hundred years, and 



208 



ANIMAL STUDIES 



probably the same is true of the crocodiles and alligators 
and some of the larger snakes. Their enemies are few, and 
death usually results when the natural course is run. 

Throughout life all reptiles periodically shed their skin, 
as birds do their feathers and mammals their fur. In the 
snakes and some of the lizards the skin at the lips loosens, 
and the animal gradually slips out of its old slough, bright 
and glossy in the new one which previously developed. In 
the others the old skin hangs on in tatters, gradually com- 
ing away as they scamper through the grass. 




Fig. 121.— Head of the lizard, or " horned toad " (Phrynosoma blanivillei), showing 
the translucent pearly scale covering the pineal eye.— From nature, by W. S. 
Atkinson. 



CHAPTEE XVIX 

.THE BIRDS 

195. Characteristics. — Birds form one of the most sharp- 
ly denned classes in the animal kingdom, and the variations 
among the different species are relatively small. " The 
ostrich or emu and the raven, for example, which may be 
said to stand at opposite ends of the series, present no snch 
anatomical differences as may be f onnd between a common 
lizard and a chameleon, or between a turtle and a tortoise," 
and these we know to be relatively slight. 

In many respects the birds resemble the reptiles, and 
long ago in the world's history the relationship was much 
closer than now, as we know from certain fossil remains in 
this country and in Europe. One of the earliest of these 
fossil birds, the Archseopteryx, is a most remarkable com- 
bination of bird and lizard. Unlike any modern bird, the 
jaws were provided with many conical reptile-like teeth. 
The wings were rather small, and the fingers, tipped with 
claws, were distinct, not grown together, as in modern birds. 
The tail was as long as the body, and many-jointed, like a 
lizard's, each vertebra carrying two long feathers. The 
bird was about the size of a crow, and it probably could 
not fly far. Other ancient types have been discovered — 
principally sea-birds — many of which existed when the 
Pacific extended over the region now occupied by the 
Eocky Mountains. These were all of the same generalized 
type, intermediate between reptile and bird. This fact 
leads us to the belief that birds descended from reptilian 

209 



210 ANIMAL STUDIES 

ancestors, and in becoming more perfectly adapted for an 
aerial life have developed into our modern forms. 

In the modern birds the most important peculiarities, 
those which separate them from all other animals, are 
correlated with the power of flight. The body is spindle- 
shaped, for readily cleaving the air. The fore limbs serve 
as wings. The hind limbs, supporting the weight of the 
body from the ground, are usually well developed. A series 
of air-chambers usually exists in powerful fliers. This 
serves a purpose analogous to that of the air-bladder of a 
fish, giving buoyancy. But the most characteristic mark 
of a bird, as above stated, is its feathers, universally present 
and never found outside the class. Like the scales of 
lizards, and probably derived from similar structures, they 
are oi different forms, and serve a variety of purposes. 
The larger ones, with powerful shafts, and forming the tail, 
act as a rudder. Those of the wings give great expanse 
with but little increase in weight, and are so constructed 
that upon the down-stroke they offer great resistance to 
the air, and push the bird forward, while in the reverse 
direction the air slips through them readily. In flight 
these movements of the wing may be too rapid for us to 
follow, as in the humming-birds, though they are usually 
much slower, two to five hundred a minute in many power- 
ful fliers, such as the ducks, and frequently long-continued 
enough to carry them many hundreds of miles at a single 
flight. The remaining feathers are soft and downy, giving 
roundness to the body and enabling it to cleave the air with 
greater ease, and, being poor conductors of heat, they aid in 
keeping the body at the high temperature characteristic of 
birds. In most birds the body is not uniformly clothed in 
feathers. Xaked spaces, usually hidden, intervene between 
the feather tracts, and on the feet and toes scales exist. 

196. Molting. — As we all know, the growth of feathers, 
unlike that of hair and nails, is limited, and after they have 
become faded and worn out they are shed, and new ones 



THE BIRDS 211 

arise to take their place. This process of molting is 
usually accomplished gradually, without diminishing the 
powers of flight ; but in the ducks and. some other birds all 
the wing- and tail-feathers drop out simultaneously, leaving 
the bird to escape its enemies by swimming and diving. 
The molting-process usually takes place in the fall, after 
the nesting and care for the young is over, and often when 
the need for a heavy winter coat commences to be felt. 
Many birds also don what are called courting colors, ruffs, 
crests, and highly colored patches, in the spring, previous 
to the mating season, doubtless for the purpose of attract- 
ing or impressing their mates. In other cases the change 
appears to be related to the bird's surroundings. A most 
beautiful example of this is the ptarmigans — grouse-like 
birds living far to the north. During winter they are per- 
fectly white and are almost invisible against the snow ; but. 
in the spring, as the snow disappears, the white feathers 
gradually fall out and new ones arise. The latter so har- 
monize " with the lichen-colored stones among which it 
delights to sit, that a person may walk through a flock of 
them without seeing a single bird." 

There are also numerous birds, chiefly those that go in 
flocks, which possess what are known as color-calls or recog- 
nition-marks. These may consist of various conspicuous 
spots or blotches on different parts of the head or trunk, 
such as we see in the yellowhammer or meadow-lark ; or 
one or more feathers of the wings or tail may be strikingly 
colored, as in many sparrows and warblers. During the 
time the bird remains at rest these usually are concealed 
under neighboring feathers, but during flight they are 
strikingly displayed. It may possibly be true, as many 
have urged, that these color-signals are for the purpose 
of enabling various members of the flock to readily follow 
their leader ; but this and many other interesting questions 
regarding the color of birds and other animals have not yet 
received final answers. 



212 ANIMAL STUDIES 

In very many animals, fishes as well as birds, the tints 
on the under side of the body are usually relatively light 
colored, shading gradually into a darker tint above. This 
is in all probability a protective device, as was recently 
shown by Mr. A. H. Thayer, an American artist. His ex- 
periments show that the light from above renders the back 
less dark, and that the shadow beneath is neutralized by 
the light color. The bird thus appears uniformly lighted, 
and this effect, together with streaks and blotches, renders 
them invisible at surprisingly short distances. 

197. Skeleton. — Turning now to the internal organization 
of birds, we find many points in common with other verte- 
brates, especially the reptiles, but many interesting modifi- 
cations are also present that adapt them for flying and for 
collecting their food. According to the nature of the food, 
the beak may have a great variety of forms. The skull may 
be thick and heavy, or thin and fragile, but these are mat- 
ters of proportion of the various parts possessed by all 
birds. The neck also is of differing length ; but it is in the 
trunk region that the greatest changes have arisen, as we 
may see in any of our ordinary birds. For example, the 
vertebrae of this part of the body are more or less fused 
together into rigid framework, to which are attached the 
ribs that in turn unite with the breast-bone. In the fliers 
the latter bears a vertical plate or keel, to which the great 
muscles that move the wings are attached. The tail con- 
sists, like that of the old-fashioned birds, of several verte- 
brae, but these are of small size and fused together into a 
little knob that supports the tail-feathers. The fore limbs 
are used for flight, but there are the same bones that exist 
in the fore limbs of other vertebrates — one for the upper 
arm, two for the lower, a thumb carrying a few feathers, 
and known as the bastard wing, and indications of several 
bones that form the hand. In the hind limb the resem- 
blance is equally apparent, though its different parts are 
of relatively large size to support the body. It is interest- 



THE BIRDS 



213 



ing to note that the knee has been drawn far up into the 
body, and that the joint above the foot is in reality the 
ankle. 

We thus see that the bird's skeleton presents the same 
general plan as that of the lizard, for example ; but in order 
to combine the elements of strength, lightness, and com- 
pactness essential to successful flight, it has been necessary 
to remodel it to a considerable degree. 

198. Other internal structures. — The lungs of birds con- 
sist of two dark-red organs buried in the spaces between the 
ribs along the back. Each communicates with extensive 
thin-walled air-sacs extending into the space between the 




intnal 
W 



LYglblfr pcd. 
HldM 

Fig. 122.— Anatomy of a bird, au., auricle ; cbl. and crb.h., cerebellum and cerebral 
hemispheres (divisions of the brain) ; duo., intestine (with portion removed) ; 
giz., gizzard; kd„ kidney; r.lng., lung; tr., trachea or windpipe; vent., ven- 
tricle. 

various organs, and in many birds of flight extending into 
the bones of the body, decreasing their specific gravity. 
" The enormous importance of this feature to creatures 
destined to inhabit the air will be readily understood when 
we learn that a bird with a specific gravity of 1.30 may 
have this reduced to only 1.05 by pumping itself full of air." 
As we know, air is taken into the body in order that the 
oxygen it contains may combine with the tissues of the 
body to liberate the energy necessary for the work of its 



214 ANIMAL STUDIES 

life. The life of birds is at high pressure, hence their need 
of much oxygen. They habitually breathe deeper breaths 
than other animals. The air passing into the body trav- 
erses the entire extent of the lung on its way back to the 
air-sacs, with the result that large quantities of oxygen are 
taken into the body. This is distributed by a circulatory 
system of a more highly developed type than in any of the 
preceding groups of animals. The ventricles of the heart 
no longer communicate with each other, and the pure and 
impure blood never mingle. Furthermore, the beating of 
the heart is comparatively rapid, rushing the oxygen as 
fast as it enters the blood to all portions of the body. The 
result is that everywhere heat is being generated, so neces- 
sary to life and activity. 

In the lower animals no special means are employed to 
husband the energy thus produced, but in the birds the 
body is jacketed in a non-conducting coat of feathers which 
prevents its dissipation. For this and other reasons the 
birds, summer and winter, maintain an even and relatively 
high temperature (102°-110°). Like the mammals, birds 
are warm-blooded animals, full of energy, restlessly active 
to an extent realized in few of the cold-blooded animals. 

199. Digestive system. — This life, at high pressure, de- 
mands a relatively large amount of food to make good the 
losses due to oxidation. The appetites of some growing 
birds is only satiated after a daily meal equal to from one 
to three times their own weight, and after reaching adult 
size the amount of daily food required is probably not less 
than one-sixth their weight. The nature of the food is 
exceedingly varied, and the digestive tract and certain ac- 
cessory structures are obviously modified in accordance 
with it. The beak, always devoid of teeth in the living 
form, varies extremely according to the work it must per- 
form. The same is true of the tongue, and many correlated 
modifications exist in the digestive apparatus. In the 
birds of prey and the larger seed-eating species, such as the 



THE BIRDS 215 

pigeons and the domestic fowls, the esophagus dilates into 
a crop, in which the food is stored and softened before being 
acted upon by the gizzard. The latter is the stomach, pro- 
vided with muscular walls, especially powerful in the seed- 
eaters, and with an internal corrugated and horny lining 
which, in the absence of teeth, serves to crush the food. In 
some species, such as the domestic fowls and the pigeons, 
this process is aided by the grinding action of pebbles 
swallowed along with the food. The remaining portions, 
with pancreas and liver, vary chiefly in length, and are 
sufficiently shown in Fig. 122 to require no further descrip- 
tion. 

200. Nesting-habits. — A few birds, such as the ostriches 
and terns, merely scoop a hollow in the earth, and make no 
further pretense of constructing a nest. On the other 
hand, some birds, such as the humming-birds and pewees, 
build wonderful creations of moss, lichens, and spider-webs, 
lining it with down, and concealing it so skilfully that 
they are not often found. Every bird has its own particular 
ideas as to the fitness of its own nest, and the results are 
remarkably different, and form an interesting feature in 
studying the habits of birds. Usually the female takes 
upon herself the choice of the nest and its construction ; 
but these duties are in some species shared by the male. 
After the eggs are laid, the male may also aid in their 
incubation, or may carry food to the female. In other 
species — for example, the pigeons and many sea-birds — the 
parents take turns in sitting upon the eggs and in the sub- 
sequent care of the young. Finally, there are certain birds, 
such as the cuckoo and cowbirds, which take advantage of 
the industry of other species and deposit an egg or two in 
the nests of the latter. All the work of incubation and 
care of the young is assumed by the foster-parents, which 
sometimes neglect their own offspring in their desperate 
attempts to satisfy the appetites of the rapidly growing and 
unwelcome guests. 



216 ANIMAL STUDIES 

The eggs of birds are relatively large, and are often 
delicately colored. In some species the blotches and streaks 
of different shades are probably protective, as in the plovers 
and sandpipers, whose eggs blend perfectly with their sur- 
roundings, but many other cases exist not subject to such 
an explanation. 

The young require a high degree of heat for their devel- 
opment, and this is usually supplied by the parent. In a 
very general way the length of sitting, or incubation, is 
proportional to the size of the egg, being from eleven to 
fourteen days in the smaller species, to seven or eight weeks 
in the ostriches. Before hatching, a sharp spine develops 
on the beak, and with this the young bird breaks its way 
through the shell. Among the quails, pheasants, plovers, 
and many other species, the }*oung are born with a covering 
of feathers, wide-open eyes, and the ability to follow their 
parents or to make their own way in the world. Such 
nestlings are said to be precocial, in distinction to the altrical 
young of the more highly specialized species, such as the 
sparrows, woodpeckers, doves, birds of prey, and their allies, 
which are born helpless and depend for a considerable time 
on the parents for support. 

Some of the owls, crows, woodpeckers, sparrows, quails, 
etc., remain in the same localities where they are bred. 
They are resident birds. Most kinds of birds, at the ap- 
proach of winter, migrate toward the southern warmer 
climes, some species traveling in great flocks, by day or 
night, and often at immense heights. In some cases this 
movement appears to be directly related to the food-supply : 
but there are many apparent exceptions to such a theory, 
and it is possible that many birds migrate for other reasons. 
Certain species migrate thousands of miles, along fairly 
definite routes, the young, sometimes at least, guided by 
the parents, which in turn appear to remember certain 
landmarks observed the year before. Sea-birds, in their 
journeys northward or southward, keep alongshore, occa- 



THE BIRDS 217 

sionally veering in to get their bearings or to rest, espe- 
cially in the presence of fogs. 

201. Classification. — Most zoologists make two primary 
divisions of the living types of birds — those like the ostrich 
with flat breast-bones, and the other the ordinary birds, in 
which the breast-bone has a strong keel for the attachment 
of the powerful muscles used in flight. This distinction is 
not of high importance, but we may use it as a convenience 
in the description of a few typical forms belonging to sev- 
eral orders into which these two divisions are subdivided. 

202. The ostriches, etc. (Ratitae). — From specimens in- 
troduced or from pictures we are doubtless familiar with 
the ostriches and with some of their relatives. The African 
ostrich (Struthio camelus, Fig. 123) is the largest of living 
birds, attaining a height of over seven feet, and is further 
characterized by a naked head and neck, two toes, and 
fluffy, plume-like feathers over parts of the body. They 
are natives of the plains and deserts of Africa, where they 
travel in companies, several hens accompanying the male. 
When alarmed, they usually escape by running with a swift- 
ness greater than that of the horse, but if cornered they 
defend themselves with great vigor by means of their 
powerful legs and beaks. Their food consists of insects, 
leaves, and grass, to which is added sand and stones for 
grinding the food, as in the domestic fowl. The American 
ostriches or rheas, are smaller ostrich-like birds, living on 
the plains of South America. Their habits are essentially 
the same as those of the African species. 

203. The loons, grebes, and auks (Pygopodes). — The birds 
in this and some of the following orders are aquatic in 
their habits. All have broad, boat-like bodies, which, with 
the thick covering of oily feathers, enables them to float 
without effort. The legs are usually placed far back on 
the body — a most favorable place for swimming, but it ren- 
ders such birds extremely awkward on land. The grebes 
are preeminently water-birds. The pied-billed grebe or dab- 




Photograph by Wil- 



THE BIRDS 219 

chick (Podilymbus podiceps), for example, found abun- 
dantly on the larger lakes and streams throughout the 
United States, captures its food, sleeps, and breeds with- 
out leaving the water. The loons living in the same situa- 
tions as the dabchick are also remarkable swimmers and 
divers. Of the three species found in this country, the 
common loon or diver (Gavia imber) attains a length of 
three feet, and is otherwise distinguished by its black 
plumage, mottled and barred with white, which is also the 
color of the under parts. The auks, murres, and puffins 
are marine, and, like their inland relatives, are expert 
swimmers and divers, strong fliers, and spend much of their 
time on the open sea. During the breeding-season they 
assemble in vast numbers on rugged cliffs along the shore, 
and lay their eggs on the bare rock or in rudely constructed 
nests. 

204. The gulls, terns, petrels, and albatrosses (Longi- 
pennes). — The birds belonging to this group are among the 
most abundant along the seacoast, and several species make 
their way inland, where they often breed. All are char- 
acterized by long, pointed wings and pigeon or swallow-like 
bodies, which are carried horizontally as the bird waddles 
along when ashore. Many are excellent swimmers and 
powerful fliers, especially the petrels and albatrosses, which 
sometimes travel hundreds of miles at a single flight. 

The gulls are abundantly represented along our coasts, 
where they frequently associate in companies, usually rest- 
ing lightly on the surface of the water, or wheeling lazily 
through the air on the lookout for food. The terns are 
of lighter build than the gulls and are more coastwise in 
their habits, and are further distinguished by plunging like 
a kingfisher for the fishes on which they live. Both the 
gulls and terns breed in colonies, every available spot over 
acres of territory being occupied by their nests, which are 
usually built of grass and weeds placed on the ground. 

The petrels and albatrosses are at home on the high 



220 



ANIMAL STUDIES 



seas, rarely coming ashore except at the breeding-season. 
Some species of the former are abundant off our shores? 
especially the stormy petrel {Procellaria pelagica) or Mother 
Carey's chickens ( Oceanites oceanicus), which, are often seen 
winging their tireless flight in the wake of ocean vessels. 
Among the dozen or so albatrosses few reach our shores. 
The wandering albatross (Diomedea exulans), celebrated in 
story and as the largest sea-bird (fourteen feet between the 
tips of its outstretched wings), is an inhabitant of the 
southern hemisphere, and only rarely extends its journeys 
to more northern regions. 

205. Cormorants and pelicans (Steganopodes). — The cor- 
morants and pelicans are comparatively large water-birds 




Fig. 124.— White pelicans (P. erythrorhynchus) and whooping-crane (Grus amen' 
cana). Photograph by W. K. Fisher. 



usually abundant along the seashore and in many sections 
of the United States. The cormorants or shags are glossy 



THE BIRDS 221 

black in color, with hooked bills, long necks, and short 
wings, which give them a duck-like flight. The much 
larger pelicans (Fig. 124) are at once distinguished by long 
bills, from which is suspended a capacious membranous sac 
All these birds are sociable in their habits, breeding, roost- 
ing, and fishing in great flocks. Their food consists of 
fishes, which the shags pursue under water and capture in 
their hooked beaks ; while the pelicans, diving from a con- 
siderable height or swimming rapidly on the surface, use 
their pouches as dip-nets. The nests, usually built of sea- 
weed or of sticks, are placed on rocky cliffs or on the 
ground in less elevated places. 

206. Ducks, geese, and swans (Lamellirostres). — The birds 
of this order, with their broad, flat, serrated beaks, short 
legs, and webbed feet, are well known, for in a wild or 
domesticated state they extend all over the earth. All are 
excellent swimmers, many dive remarkably well, and are 
strong on the wing. While a considerable number breed 
within the United States, their nesting-grounds are gener- 
ally farther north, and in the early spring it is not unusual 
to see them migrating in flocks from their warmer winter 
homes. Among the ducks, the mergansers, mallards (from 
which our domestic species have been derived), the teals, 
and the beautiful wood-duck remain with us the year 
round, dwelling on quiet streams and shallow ponds, living 
on fish, Crustacea, and seeds. In the more open waters 
of the larger lakes and along the seacoast we find the can- 
vasback, the scaup-ducks, and the eiders which supply the 
famous down of commerce. Of the few species of geese 
which inhabit the United States, the Canada goose (Branta 
canadensis) is perhaps the most familiar. During their 
migrations to the nesting sites they fly in V-shaped flocks, 
their "honks" announcing the opening of spring. The 
brant (B. bernicla) is also common in the eastern part of 
the country, where it, like its relations, lives on vegetable 
substances entirely. The swans are familiar in their semi- 



222 ANIMAL STUDIES 

domesticated state, but the two beautiful wild swans found 
in this country are rarely seen. 

207. The herons and bitterns (Herodiones). — The herons 
and bitterns are also aquatic in their habits, but, unlike the 
swimming-birds, they seek their food by wading. Adapting 
them for such an existence, the legs and neck are usually 
very long, and the bill, longer than the head, is sharp and 
slender. Among the relatively few species in the United 
States, the great blue heron (Ardea hcrodias) is widely dis- 
tributed, and may often be seen standing motionless in 
some shallow stream on the lookout for fish, or it may 
wander away into the meadows and uplands to vary its diet 
with frogs and small mammals. Even more familiar is the 
little green heron or poke {Ardea virescens), which also is 
seen widely over the country. The night-herons, as their 
name indicates, stalk their prey by night, and during the 
day roost in companies — a characteristic common to most 
herons. The bitterns or stake-drivers are at home in reedy 
swamps, where they live singly or in pairs, and throughout 
the night, during times of migration, utter a booming noise 
resembling the driving of a stake into boggy ground. As 
a rule, the herons breed as they roost — in companies — build- 
ing bulky platforms, usually in trees. The bitterns, on the 
other hand, secrete their nests on the ground in the rushes 
of their marshy home. 

208. Cranes, rails, and coots (Paludicolae). — In their ex- 
ternal form the cranes and rails resemble the herons, but 
in their internal orgrnization they differ considerably. 
They likewise inhabit marshy lands, but usually avoid 
wading, picking up the frogs, fish, and insects or plants 
along the shore or from the surface of the water. The cranes 
are comparatively rare in this country, yet one may occasion- 
ally meet with the whooping-cranes {Grus amerieana) and 
sand-hill cranes (Grus mexicana), especially in the South 
and West. They are said to mate for life, and annually 
repair to the same breeding-grounds, where they build their 



THE BIRDS 223 

nests of grass and weeds on the ground in marshy places. 
The rails are more abundant, though rarely seen on ac- 
count of their habit of skulking through the swamp 
grasses. Only rarely do they take to the wing, and then 
fly but a short distance, with their legs dangling awk- 
wardly. Closely related to them are the coots or mud-hens 
(Fulica americana), which may be distinguished, however, 
by their slaty color, white bills, and lobed webs on the toes, 
and consequent ability to swim. All over the United 
States they may be seen resting on the shores of lakes or 
quiet streams, or swimming on the surface gathering food. 
The nest consists of a mass of floating reeds, which the 
young abandon almost as soon as hatched. 

209. The snipes, sandpipers, and plovers (Limicolse). — The 
snipes, sandpipers, and plovers are usually small birds, 
widely scattered throughout the country wherever there 
are sandy shores and marshes. In most species the legs 
are long, and in connection with the slender, sensitive bill 
fit the bird for picking up small animals in shallow water 
or probing for them deep in the mud. During the greater 
part of the year they travel in flocks, but at the nesting- 
season disperse in pairs and build their nests in shal- 
low depressions in the earth. The eggs are usually 
streaked and spotted, in harmony with their surroundings, 
as are the young, which leave the nest almost as soon as 
hatched. 

Fully fifty species of these shore-birds live within the 
confines of the United States. Among these the woodcock 
(Philoliela minor) and snipe ( Gallinago delicala) are abun- 
dant in many places inland, where they probe the moist soil 
for food, and in turn are eagerly sought by the sportsman. 
Even more familiar are the sandpipers and plovers, which 
are especially common along the seacoast, and are also 
abundantly represented by several species far inshore. 
Among the latter are the well-known spotted sandpiper or 
"tip-up" (Actitis macularia) and the killdeer plover {^Egi- 



224 



ANIMAL STUDIES 



alitis vocifera), which inhabit the shores of lakes and 
streams throughout the country. 

210. Quail, pheasants, grouse, and turkeys (Gallinas). — The 
quail, grouse, and our domestic fowls are all essentially 




Fig, 105. — California quail {Lophortyx califomicus). Two-thirds natural size. 

ground-birds, and their structure well adapts them to such 
a life. The body is thick-set, the head small, and the beak 
heavy for picking open and crushing the seeds and berries 



THE BIRDS 225 

upon which they live. The legs and feet are stout, and 
fitted for scratching or for running through grass and 
underbrush. Frotective colors also prevent detection, but 
if close pressed they rise iuto the air with a rapid whirring 
of their stubby wings, and after a short flight settle to the 
ground again. During the breeding-season the male usu- 
ally mates with a number of hens, which build rough nests 
in hollows in the ground, where they lay numerous eggs. 
The young are precocial. 

The quail or bob-white {Colinus virginianus) and the 
ruffed grouse (Bonasa umbellus) occur throughout the 
Eastern States. Over the same area the wild turkey 
(Meleagris gallopavo) once extended, but is now almost 
extinct. The prairies of the middle West support the 
prairie-hen (Tympanuchus americanus), and the valleys 
and mountains of the far West are the home of several 
species of quails, some of which are beautifully crested. 

211. Pigeons and doves (Columbse). — The pigeons and 
doves belong to a small yet well-defined order, with upward 
of a dozen representatives in the United States. They are 
of medium size, with small head, short neck and legs, and 
among other distinguishing characters frequently possess a 
swollen, fleshy pad in which the nostrils are placed. In 
former years the passenger-pigeon (Ectopistes migratorius), 
inhabiting eastern North America, was probably the most 
common species in this country. Their flocks contained 
thousands, at times millions, of individuals, which often 
traveled hundreds of miles a day in search of food, to return 
at night to definite roosts — a trait which enabled the hunter 
to practically exterminate them. At present the mourning- 
or turtle-dove (Zenaidura macroura) is the most familiar 
and wide-spread of the wild forms. The domestic pigeons 
are all descendants of the common rock-dove (Columla 
livid) of Europe, the numerous varieties such as the tum- 
blers, fantails, pouters, etc., being the product of man's 
careful selection. In the construction of the nest, usually 



226 ANIMAL STUDIES 

a rude platform of twigs, and in the care of the young 
both parents have a share. The young at hatching are 
blind, naked, and perfectly helpless, and are fed masticated 
food from the crops of the parents until able to subsist on 
fruits and seeds. 

212. Eagles, hawks, owls, etc. (Raptores). — The birds of 
prey, all of which belong to this order, are carnivorous, 
often of large size and great strength, and are widely dis- 
tributed throughout this country. The vultures live on 
carrion, some of the small hawks and owls on insects, while 
the majority capture small birds and mammals by the aid of 
powerful talons. In every case the beak is hooked, and the 
perfection of the organs of sight and hearing is unequaled 
by any other animal, man included. They live in pairs, 
and in many species mate for life. As a rule, the female 
incubates the eggs, and the male assists in collecting 
food. 

Among the vultures, the turkey-buzzard ( Cathartes aura) 
is most abundant throughout the United States, especially 
in the warmer portions, where it plays an important part 
as a scavenger. Of the several species of hawks, the white- 
rumped marsh-hawk (Circus hudsonius), the red-tailed 
hawk (Buteo borealis), the red-shouldered hawk (Buteo 
Uneatus), and above all the bold though diminutive spar- 
row-hawk (Falco sparverius) are the most abundant and 
familiar. In the more unsettled regions live the golden 
eagle (Aquila chrysaetus) and bald eagle (Haliaetus leuco- 
cep/talus). The owls are nocturnal, and not so often seen 
as the other birds of prey, yet the handsome and fierce 
barn or monkey-faced owl (Strix pratincola), and the larger 
species, such as the great gray owl (Scotiaptex cincreua), 
and the beautiful snowy owl (Xyctea nyctea), are more or 
less common, and occasionally seen. Much more abundant 
is the little screech-owl (Megascops asio), and in the AVest- 
ern States the burrowing-owl {Speotyto cunieularia), which 
lives in the burrows of the ground-squirrels and prairie- 



THE BIRDS 227 

dogs. Fiercest and strongest of the tribe is the great 
horned owl (Bubo virginianus). 



Fig. 126.— Golden eagle (Aquila chrysaetus). 

213. Cuckoos and kingfishers (Coccyges). — Omitting the 
order of parrots (Psittaci), whose sole, representative in this 
country is the almost exterminated Carolina parrakeet 



228 ANIMAL STUDIES 

(Conurus carolinensis), we next arrive at the cuckoos and 
kingfishers, which differ widely in their habits. The black- 
or yellow-billed cuckoos or rain-crows are shy, retiring 
birds, with drab plumage, and though seldom seen are often 
fairly abundant, and are of much service in destroying 
insects. Unlike their shiftless European relatives, which 
lay their eggs in the nests of others birds, they build their 
own airy homes in some bush or hedgerow, and raise their 
brood with tender care. The belted kingfisher (Ceryle 
alcyori) is also of a retiring disposition, and spends much 
of its time on some branch overlooking the water, occa- 
sionally varying the monotony by dashing after a fish, or 
flying with rattling cry to another locality. Their nests 
are built in holes in banks, and six or eight young are 
annually reared. 

214. The woodpeckers (Pici). — The woodpeckers are 
widely distributed throughout the world, and are preemi- 
nently fitted for an arboreal life. The beak is stout for 
chiseling open the burrows of wood-boring insects, which are 
extracted by the long and greatly protrusible tongue. The 
feet, with two toes directed forward and two backward, are 
adapted for clinging, and the stiff feathers of the tail serve 
to support the bird when resting. Almost all are bright- 
colored, with red spots on the head, at least in the males, 
which may further attract their mates by beating a lively 
tattoo with their beaks on some dry limb. The glossy 
white eggs are laid in holes in trees, and both parents are 
said to share the duties of incubation and feeding the 
voung. Among the more abundant and well-known species 
is the yellowhammer or flicker {Colaptes auratus), which 
extends throughout the United States. Somewhat less 
widely distributed is the red-headed woodpecker {31 da Her- 
pes eryt7irocephahis), and the small black-and-white downy 
woodpecker (Dryolates pubescens). This is often called 
sapsucker, but incorrectly so, as, like all but one of our other 
woodpeckers it feeds on insects. The yellow-bellied wood- 



THE BIRDS 



229 



pecker (Sp7iyrapicus varius) is a real sapsucker, living on 
the juices of trees. A close relative of the red-headed 
woodpecker, the California woodpecker (Melanerpes formi- 
civorus), is renowned for its habit of boring holes in bark 
and inserting the acorns of the live oak. Subsequently the 
bird returns, and breaking open the acorns, devours the 
grubs which have infested them, and apparently eats the 
acorns also. 

215. Swifts, humming-birds, etc. (Macrochires). — The birds 
of this order are rapid, skilful fliers, and their wings are 
very long and pointed. The feet, on the other hand, are 




Fig. 127.— Night-hawk ( Chordeiles virginianus) on nest. Photograph by H. K. Job. 

small, relatively feeble, and adapted for perching or cling- 
ing. Accordingly, the insects upon which they feed are 
taken during flight by means of their open beaks. The 
night-hawk (Chordeiles virginianus), roosting lengthwise on 
a branch by day, at nightfall takes to the wing, and high 
in the" air pursues its food after the fashion of a swallow. 
In the same haunts throughout the United States the whip- 



230 ANIMAL STUDIES 

poorwill (Antrostomus vociferus) occurs, sleeping by day, 
but active at night. Xeither of these birds constructs nests, 
but lays its streaked and mottled eggs directly on the 
ground. The chimney-swifts (Ohcetura pelagica), swallow- 
like in general form and habits, but very unlike the swallows 




Fig. 128.— Anna hummers Cone day old), showing short hill and small size of body. 
Compare with last joint of little finger. 

in structure, frequent hollow trees or unused chimneys, to 
which they attach their shallow nests. The nearly related 
humming-birds are chiefly natives of tropical America, only 
a few species extending into the United States. Of these 
the little, brilliantly colored, and pugnacious ruby throat 
(TrocJulus colubris) is the most widely distributed. Its 
nest, like that of other hummers, is composed of moss and 
lichens bound together with cobweb and lined with down. 

216. Perching birds (Passeres). — The remaining birds, 
over six thousand in all, belong to one order, the Passeres 
or perchers. They are characterized by great activity, 
interesting habits, frequently by exquisite powers of song, 
and in addition to several other structural arrangements 
have the feet adapted for perching. Their nesting habits 



THE BIRDS 



231 



differ widely, but in every case the young are helpless at 
the time of hatching, and require the care of the parents. 

The perchers constitute the greater number of the birds 
living in the meadows and woods, and are more or less 




Fig. 129.— Anna hummer (Calypte anna) on nest. 

common, and consequently familiar everywhere. Among 
the families into which the order is divided that of the fly- 
catchers (Tyrannidce), the crows and jays (Corvidce), the 
orioles and blackbirds (Icteridce), the finches and sparrows 
(Fringillidce), the swallows (Hirwidinidce), the warblers 
{Mniotiltidce), the thrushes, robins, and bluebirds ( Turdidce), 
are the more familiar, though the others are equally inter- 
esting. 



CHAPTEE XVIII 

THE MAMMALS 

217. General characteristics. — The mammals, constituting 
the last and highest class of the vertebrates, comprise such 
forms as the opossum and kangaroo, the whales and por- 
poises, hoofed and clawed animals, the monkeys and man. 
All are warm-blooded, air-breathing animals, having the 
skin more or less hairy. The young are born alive, except 
in the very lowest forms, which lay eggs like reptiles, and 
for some time after birth are nourished by milk supplied 
from the mammary glands (hence the word mammals) of 
the mother. The skeleton is firm, the skull and brain 
within are relatively large, and, with few exceptions, four 
limbs are present. 

Most of the mammals inhabit dry land. A number, 
however, such as the whales and seals, are aquatic ; while 
others, such as the beavers, muskrats, etc., though not 
especially adapted for an aquatic life, are, nevertheless, 
active swimmers, and spend much of their time in the 
water. 

Mammals tend to associate in companies, as we may 
witness among the ground-squirrels, prairie-dogs, rats, 
mice, and the seals and whales. In many cases they band 
for mutual protection, and often fight desperately for one 
another. Claws, hoofs, and nails are efficient weapons, and 
spiny hairs, as on the porcupines, bony plates, such as 
encircle the bodies of the armadillos, and thick skin and 
hair, serve as a protection. The hair is also frequently 
colored to harmonize the animal with its surroundings. 



THE MAMMALS 233 

Some rabbits and hares in the far north don a white coat 
in the winter season. 

218. Skeleton. — As in other vertebrates, the external 
form of mammals is dependent in large measure upon the 
internal skeleton. This consists of relatively compact 
bones, the cavities of which are filled with marrow. Those 
forming the skull are firmly united, and, as in other verte- 
brates, afford lodgment for several organs of special sense 
and for the brain, which, like that of the birds, completely 
fills the cavity in which it rests. The vertebral column to 
which the skull is attached differs considerably in length, 
but it invariably gives attachment to the ribs, and to the 
basal girdles supporting one or two pairs of limbs. Gener- 
ally speaking, the number of bones in the head and trunk 
of all mammals is the same, so the variations we note in 
the species about us, for example, are simply due to differ- 
ences of shape and proportion. As we are aware, there is a 
great dissimilarity between the length of the neck of man 
and that of the giraffe, yet the number of bones in each 
is precisely the same. On the other hand, the variations 
occurring in the limbs are often due to the actual disap- 
pearance of parts of the skeleton. Five digits in hand 
and foot is the rule, and yet, as we well know, the horse 
walks on the tip of its middle finger and toe, the others 
being represented by small, very rudimentary, splint bones 
attached far up the leg. The even-hoofed animals walk on 
two digits, two smaller hoofed toes being often plainly 
visible a short distance up the leg, as in the pig. In the 
whales the hind limbs have completely disappeared, and in 
the seals, where the fore limbs are modified, as in the 
whales, into flippers, the hind limbs show many signs of 
degeneration. 

219. Digestive system. — Some mammals, such as man, 

monkeys, and pigs, are omnivorous ; others, like the cud- 

chewers and gnawers, are vegetarians ; and still others, 

like the foxes, weasels, and bears, are carnivorous. In 

16 



234 ANIMAL STUDIES 

every case the food substances are acted on by a digestive 
system constructed on the same general plan as that in man, 
yet modified according to the specific work it is required to 
perform. The teeth especially afford a valuable indication 
of the animal's feeding habits, and, as we may notice later, 
are also of much value in classification. They consist of 
incisors used in biting, canines for tearing, and premolars 
and molars for crushing and grinding. 

The remaining portions of the digestive tract, esopha- 
gus, stomach, and intestine, with their appended glands, are 
usually not unlike those possessed by the squirrel. The 
chief differences are in the size of the various regions. 
The stomach, for example, may be long and slender or of 
great dimensions, and its surface may further be increased 
by several lobes, which are especially well developed in the 
ruminants or cud-chewers. The intestine, relatively longer 
in the mammals than in any other class of vertebrates, also 
exhibits great differences in length and size. In the flesh- 
eating species its length is about three or four times the 
length of the body, while in the ruminants it is ten or 
twelve times the length of the animal. 

220. Nervous system and sense-organs. — As before noted, 
the nervous system of mammals is characterized by the 
large size and great complexity of the brain. Even in the 
simpler species the cerebral hemispheres (large front lobes 
of the brain) are well developed, and in the higher forms 
of the ascending series they form by far the larger part 
of the brain. The sense-organs also are highly developed, 
and are constructed and located much as they are in man. 
The greatest variations occur in the eyes. In some of 
the burrowing animals they are usually small, and in some 
of the moles and mice may even be buried beneath the 
skin and very rudimentary. On the other hand, they are 
large and highly organized in nocturnal animals ; more 
so, usually, than in those which hunt their prey by day. 
The ears also have different grades of perfection, which 



THE MAMMALS 235 

appear to be correlated with the habits of the animal. 
Among the species of subterranean habits the sense of hear- 
ing is largely deficient ; but, on the other hand, it is ex- 
ceedingly keen in the ruminants, and enables them to detect 
their enemies at surprisingly great distances. In these 
creatures the outer ears are of large size and great mobility, 
and, placed as they are on the top of the head, serve to con- 
centrate the sound-waves on the delicate apparatus within. 
In the mammals the sense of smell reaches its highest de- 
velopment, especially among the carnivores which scent their 
prey. On the other hand, it is said to be absent in the 
whales and very deficient in the seals. The sense of taste, 
closely related to that of smell, is located in taste-buds on 
the tongue, and is also more acute than in any other class of 
animals. The sense of touch, located over the surface of 
the body, is especially delicate on the tips of the fingers, 
the tongue, and lips, which often bear long tactile hairs, 
called whiskers or vibrissa. 

221. Mental qualities. — Correlated with the high degree 
of perfection of the brain and sense-organs the mammals 
show a higher degree of development of the intellectual 
faculties than any other class of animals. In many cases 
their acts are instinctive, and not the result of previous 
training and experience. Just as the duck hatched in an 
incubator instinctively takes to the water and pecks at its 
food, or as the bee builds its symmetrical comb, many of 
the mammals perform their duties day by day. On the 
other hand many other mammals are also undoubtedly in- 
telligent. They possess the faculty of memory ; they form 
ideas and draw conclusions ; they exhibit anger, hatred, and 
self-sacrificing devotion for their companions and offspring 
that is different from that in man only in degree and not 
in kind. In fact, intelligence differs from instinct primar- 
ily in its power of choice among lines of action. 

222. Classification. — Of the eleven orders into which the 
mammals have been divided eight are represented in this 




Fig. 130.— Three-toed sloth {Bradypus). About one-tenth natural size. 



THE MAMMALS 



237 



country. Of the other three the first {Monotremes) and 
simplest of the eleven is represented by the duck-mole 




Fig. 131.— Australian duck-mole (Or?iithorhynchus paradoxus). One-fifth natural 
size. 

(Ornithorhynchus) living in the Australian rivers. Its 
general appearance and mode of life are illustrated in 




—The manatee, or sea-cow (Trichechus latirostris). A livin 
cow related to the now extinct Steller's sea-cow. 



; tpecies oi' Bear 



THE MAMMALS 



239 



Fig. 131. The duck-moles are the only mammals which 
lay eggs. These are deposited in a carefully constructed 
nest where the young are hatched. Another order (Eden- 
tata) includes a number of South and Central American 
forms, among which are the ant-eaters, armadillos, and tree- 
inhabiting sloths (Fig. 130). Still another order (Sirenia) 
includes the fish-shaped marine dugong and sea-cows or 
manatees (Fig. 132), of which one species is found occasion- 
ally on the Florida coast. The remaining orders are de- 
scribed in the succeeding sections. 

223. The opossums and kangaroos (Marsupialia).— The 
lowest order of mammals represented in the United States 




Fig. 133.— Opossum (Didelphys Virginian a). One-tenth - natural size. Photograph 
by W. H. Fisher. 

is that of the marsupials. It includes the opossums and 
kangaroos, together with a number of comparatively small 
and unfamiliar animals living chiefly in and about Australia. 



240 ANIMAL STUDIES 

The opossums, fairly abundant throughout the warmer 
portions of this country, are rat-like creatures, with scaly 
tails, yellowish-white fur, large head, and pointed snout. 
Except at the breeding season they lead solitary lives, 
sleeping in the holes of trees by day and at night feeding 
on roots, birds, and fruits. 

The kangaroos, familiar from specimens in menageries 
or museums, chiefly inhabit the plains of Australia. The 
giant gray kangaroos (Macropus giganteus), attaining a 
height of over six feet, go in herds, and owing to the great 
development of their hind limbs and tails are able, when 
alarmed, to travel with the swiftness of a horse. Several 
smaller species, some no larger than rabbits, live among 
the brush, and like their larger relatives crop the grass and 
tender herbage with sharp incisor teeth. 

While the marsupials do not lay eggs as does the duck- 
mole, they allow them to develop within the body for a 
very short time only. Hence the young, when born, are 
scarcely more than an inch in length, and are blind, naked, 
and perfectly helpless. At once they are placed by the 
mother in the pouch of skin, or marsupium, on the under 
side of her body. In this the young are suckled and pro- 
tected until able to gather their own food and fight their 
own way. 

224. Rodents or gnawers (Glires). — The rodents are a 
large group of mammals, including such forms as the rats, 
mice, squirrels, gophers, and rabbits. They are readily dis- 
tinguished by their clawed feet adapted for climbing or 
burrowing, and by large curved incisor teeth. Unlike 
ordinary teeth, they grow continually, and, owing to the 
restriction of the hard enamel to their front surfaces, wear 
away behind faster than in front, thus producing a chisel- 
like cutting edge. 

The largest of our native rodents is the porcupine 
(Eretliizon dorsatus), which ranges from Maine to Mexico, 
and attains a length of nearly three feet. Many of the hairs 



THE MAMMALS 



241 



of the body have the form of stiff, barbed spines (Fig. 134), 
readily dislodged so that the animal requires no other wea_ 
pon of defense. The rabbits and hares are of smaller size, 
and the cottontails especially are widely distributed. West 
of the Mississippi the jack-rabbits are familiar, and are 




Fig. 134. —Porcupine (Hystrix cristata). One-tenth natural size. — After Brehm. 

famous for their great speed. Like the porcupines, they 
feed on leaves and grass, and are often very destructive. 
The mice, especially the field and white-footed mice, are 
abundant in woodland and meadow throughout the United 
States. The house-mouse (Mus musculus) is a native of 
Europe, as is the common rat (M. decumanus), which was 
imported over a century ago. The wood-rat (Neotoma), 
however, is native, and may be found in many localities 
from east to west. The muskrat {Fiber zibethicus), beaver 
(Castor canadensis), and woodchuck (Arctomys monax) were 
also more or less plentiful formerly, but in many localities 
are well-nigh exterminated. The squirrels, on the other 
hand, continue to exist in large numbers. The prairie- 



242 ANIMAL STUDIES 

dogs, ground-squirrels, and chipmunks of the terrestrial 
spacies are of frequent occurrence, and of the tree-dwellers 
the fox, gray and red squirrels are well known in many 
sections of the United States. 

225. Insect-eating mammals (Insectivora) . — The shrews 
and moles belonging to this order arc representatives of a 
large group of small animals, which, unlike the major 
number of rodents, live on insects. The shrews, of which 
there are several species in this country, are small, mouse- 
like creatures, nocturnal in their habits, and hence rarely 
seen. The moles are of much larger size, and owing to 
their burrowing proclivities scarcely ever appear above 
ground, but excavate elaborate burrows with their shovel- 
like feet, devouring the insects which fall in their way. The 
common mole {Scalops aquaticus) extends from the eastern 
seaboard to the Mississippi Eiver, where it is replaced by 
the prairie-mole (S. argenteus), which extends far to the 
west, into a country inhabited by other species. 

226. The bats (Cheiroptera). — The bats are also insectiv- 
orous, but their habits are widely different from those of 
the shrews and moles. The forearm and the fingers of the 
fore limbs are greatly elongated, and are connected by a 
thin papery membrane, which also includes the hind limbs 
and tail, and serves as an efficient organ of flight. During 
the day they remain suspended head downward in some 
dark cranny, awakening at nightfall to capture flying 
insects. Several species are found in this country, the 
most common being the little brown bat ( Vcsperfilio fus- 
cus), with small, fox-like face, large erect ears, and short 
olive-brown hair. The red bat (Lasiurus borealis) is also 
plentiful everywhere throughout the United States, and is 
distinguished from the preceding by its somewhat larger 
size and long reddish-brown fur. 

227. The whales and porpoises (Cete).— The animals 
belonging to this order, the whales (Fig. 135), porpoises, and 
dolphins, are aquatic animals bearing a resemblance to fishes 



THE MAMMALS 



243 



only in external form. The cylindrical body has no distinct 
neck, the comparatively large head uniting directly with 





m 

I 
H 
■ 

■ 



the cylindrical body, which terminates in the tail with hori- 
zontally placed fins. No external signs of hind limbs exist, 



244 ANIMAL STUDIES 

while the fore limbs are short and capable of being moved 
only as a whole. External ears are also absent. The eyes 
are exceedingly small, those of individuals attaining a length 
of from fifty to eighty feet, being in some species, at least, 
but little larger than those of an ox. These are often placed 
at the corners of the mouth. The nasal openings, often 
known as blow-holes, are situated on the forehead, and as 
the whale comes to the surface for air afford an outlet for 
the stream of breath and vapor often blown high in the 
air — a process known as spouting. In some of the whales, 
such as the dolphin, porpoise, and sperm-whales, the teeth 
persist throughout life, but in most of the larger species 
they never " cut " the gum, but early disappear, and their 
place is taken by large numbers of whalebone plates with 
frayed edges which act as strainers. The smaller-toothed 
forms (porpoises, dolphins, and several species of grampus) 
are frequently seen close to the shore, where they are usu- 
ally actively engaged in capturing fish. On the other hand, 
the larger species, such as the humpback, right whale, and 
sulfurbottom, not uncommon along our coasts, especially 
to the northward, live on much smaller organisms. With 
open mouth these whales swim through the water until 
they collect a sufficient quantity of jelly-fishes, snails, and 
Crustacea, then closing the mouth strain out the water 
through the whalebone fringes and swallow the residue. 

As noted above, the animals of this order are almost 
wholly devoid of hair, but the heat of the body is retained 
by a thick layer of fat beneath the skin. This " blubber " 
also gives lightness to the body (as do the voluminous lungs), 
and, furthermore, yields large quantities of oil, which in 
former times made "whale-fishing " a profitable industry. 
The whales bear one, rarely two offspring, which are solicit- 
ously attended by the mother for a long time. The smaller 
species grow to a length of from five or eight feet (por- 
poises, dolphins) to twice this size (grampuses) ; while the 
larger whales, by far the largest of animals, range from 



THE MAMMALS 245 

thirty to oyer a hundred feet in length with a weight of 
many tons. 

228. Hoofed mammals (TJngulata).— The. order of hoofed 
animals or ungulates includes a large number of forms like 
the zebra, elephant, hippopotamus, giraffe, deer, and several 
other wild species, some of which are domesticated, such 
as horses, sheep, goats, and cattle. All of these animals 
walk on the tips of their toes, and the claws have become 
developed into hoofs. The order is divided into the odd- 
toed forms (perissodactyls), such as the rhinoceros with 
three toes and the horse with one, and the even-toed (artio- 
dactyls), as the pigs with four, and the ox, deer, etc., with 
two toes. The even-toed forms are again divided into 
those which chew the cud (ruminants) and those which do 
not (non-ruminants). No living native odd-toed mammal 
exists in this country, and of the wild even-toed species all 
are ruminants. In the members of this latter group the 
swallowed food passes into a capacious sac (the paunch), is 
thoroughly moistened, and passed into the second division 
(the honeycomb), later to be regurgitated and ground by 
the powerful molars. It is then reswallowed, and under- 
goes successive treatment in the other two divisions of 
the stomach (the manyplies and reed) before entering the 
intestine. 

Among the North American ruminants, the deer 
family (Cervidce) is the best represented. In the more 
unsettled regions of the East the red deer is still com- 
mon, and the same may be said of the white-tailed, black- 
tailed, and mule-deer of the West. Among the woods 
and lakes to the northward live the reindeer and caribou, 
and the largest of the deer family, the moose, which 
attains the size of the horse. Of nearly the same size is 
the wapiti or elk. In all of the above-mentioned species 
the horns, if present, are confined to the male (except 
in the reindeer), and are annually shed after the breeding 
season. 



246 ANIMAL STUDIES 

The native hollow-horned ruminants (Bovidce) are at 
present confined to the Western plains, and comprise the 
pronghorn antelope {Antilocapra americana), the wary big- 
horn or Rocky Mountain sheep ( Ovis canadensis), living in 
mountain fastnesses, and the buffalo or bison (Bison ameri- 
canus). All of these species were formerly abundant, 
especially the pronghorn and buffalo, which roamed the 
plains by thousands, but their extermination has been 
nearly complete, small herds only persisting in a few wild, 
inaccessible regions, or protected in parks. 

Our domestic sheep and cattle are probably the descend- 
ants of several wild species living in Europe and other 
portions of the world. Of the domesticated ungulates the 
horse is the direct descendant of Asiatic wild breeds ; while 
the pig traces its ancestry back to the wild boar {Sus scrofa) 
of Europe, and probably a native species (S. indicus) of 
eastern Asia. 

229. Flesh-eating mammals (Ferae). — The order of Fera 
or Carnivora is typically exemplified by such animals as the 
lions, tigers, bears, dogs, cats, and seals, forms which differ 
from all other mammals by the large size of the canine teeth 
(often called dog-teeth) and the molars, which are adapted 
for cutting, not crushing. The limbs, terminated by four 
or five flexible digits, bear well-developed claws, which, to- 
gether with the teeth, serve for tearing the prey. While 
the bears shuffle along on the soles of their feet, the greater 
number of species, as illustrated by the dog and cat, tread 
noiselessly on tiptoe. Almost all are fierce and bold, with 
remarkably keen senses and quick intelligence, and are the 
dreaded enemies of all other orders of mammals. 

The largest land-inhabiting carnivora are the bears, of 
which the brown or cinnamon bear (Ursus americana s), 
inhabiting Xorth America generally where not extermi- 
nated, and the huge grizzly ( Ursus horribilis) of the West- 
ern mountains, are the best-known species. The former 
lives on berries and juicy herbs, while the grizzly prefers 



THE MAMMALS 



247 



the flesh of animals which it kills. The raccoon (Fig. 136) 
(Procyon lotor) is found in wooded districts all over the 
United States, and its general appearance and thieving 
propensities are well known. Almost everything is accept- 




able as an article of food, and its fondness for poultry and 
vegetables makes it an unmitigated nuisance. The otters, 
skunks, badgers, wolverenes, sables, minks, and weasels, while 
differing considerably in general appearance and habits, nev- 



248 



ANIMAL STUDIES 



ertheless belong to one family (the weasel family, Mustelida), 
and are more or less valued for their fur. Almost all are 
characterized by a fetid odor, especially the skunk, which 
is notoriously offensive, and in consequence is avoided by 
all other animals. 

The dog family is represented by several widely distrib- 
uted varieties of the red fox ( Vulpes pennsylva?iicus) and 
gray fox ( Urocyon cinereo-argentatus), and by the coyotes 

— 




-Silver fox {Vulpes pennsylvanicus, var. argentatus). 
by W. K. Fishsb. 



Photograph 



{Canis latrans) and wolves (Canis nulilus). The domestic 
dog (Canis familiaris) is probably the descendant of the 
wolf, and owing to man's careful breeding during thou- 
sands of years has formed several widely differing varieties. 
The cat family, comprising the most powerful, savage, 
and keenest-scented carnivora, is represented by the lion, 
tiger, jaguar, and hyena. In this country the group is 
represented by the lynx (Lynx canadensis), the wildcat 
(Lynx rufus), and the panther or puma (Fells concolor), 
which attains the length of nearly five feet. The domestic 
cat has, like the dog, been domesticated for centuries, and 
has possibly descended from an African species (Felis 




Fig. 138.— Panthers (Felis concolor) and peccaries (Dicotyles torquatus). 
17 



250 



AXIMAL STUDIES 



caffra), which was held sacred by the Egyptians, who em- 
balmed them by thousands. 

230. Man-like mammals (Primates). — The last and high- 
est order of mammals, the Primates, includes the lemurs, 
monkeys, and man. The first of these are strange squir- 
rel-like forms living chiefly in trees in Madagascar and 
neighboring regions where they feed on insects. The apes 
and monkeys are divided into Old and Xew World forms, 
which differ widely from each other. The American species 
are marked by flat noses, with the nostrils far apart. All are 
arboreal, many have long prehensile tails, and the digits bear 
nails, not claws. Among them are several species of marmo- 
sets, the howling monkeys (Jfyocetes), the spider-monkeys 
(Ateles), and the capuchins (Cebus), all of which are more or 
less common in captivity. In the Old World apes, on the 
other hand, the nostrils are close together and are directed 
downward, the tail is never 
prehensile, and in some cases 
is rudimentary, and may even 
disappear. The lowest spe- 
cies (the dog-like apes) in- 
clude the large, clumsy ba- 
boons, among them the fa- 
miliar blue-nosed mandrill 
(CynocejjJialus maimon) and 
several other species of light- 
er frame, such as the long- 
tailed monkey (Cercopithe- 
cus) (Fig. 140), the tailless 
Macacus, common in menag- 
eries, and the Barbary ape, in- 
habiting northern Africa and 
extending over into Spain. 

The remaining anthro- 
poid or man-like apes include the gibbons (Hylobates), orang- 
utan (Simia), gorilla (Gorilla), and chimpanzee (Anthropo- 




Fig. 139.— Baby orang-utan. From life. 




Fig. 140.— A monkey ( Cercopithecus) in a characteristic attitude of watchfulness. 



252 



ANIMAL STUDIES 



pitJiecus). The gibbons, inhabiting southeastern Asia, pos- 
sess arms of such length that they are able to touch their 
hands to the ground as they stand erect. They are thus 
adapted for a life in the trees, where they spend most of their 
time feeding on fruit, leaves, and insects. In the same dis- 
trict the orang occurs, walking when on the ground on its 
knuckles and the sides of its feet. It prefers the life in 
the trees, however, in 
which it builds nests 
serving for rest and 
concealment. The go- 
rilla (Fig. 140), the 
largest of apes, attain- 
ing a height of over 
five feet and a weight 
of two hundred 
pounds, is a native of 
Africa, where it lives 
in families and sub- 
sists on fruits. The 
same region is the 
home of the chimpan- 
zee, which in its vari- 
ous characteristics ap- 
proaches most nearly 
to man. 

Man {Homo sajri- 
ens) is distinguished 

by the inability to oppose the big toe as he does his thumb — 
a feature associated with his erect position — and by the rela- 
tively enormous size of the brain. Even in an average four- 
year-old child or an Australian bushman the brain is twice as 
large as in the gorilla. With this relatively great develop- 
ment of the nervous system is correlated superior mental 
faculties, which together with social habits and powers of 
speech exalt man to a position far above the highest ape. 




Fig. 141.— Gorilla (Gorilla). 



THE MAMMALS 25 3 

As usually understood, the family of man (Hominidce) 
contains but a single species, cosmopolitan and highly vari- 
able. This species is "now split up into many subspe- 
cies or races, the native man of this continent, or ' Ameri- 
can Indian,' being var. americanus. Other races now 
naturalized in America are : the Caucasian race, var. euro- 
pcBUs; the Mongolian race, var. asiaticus; and the negro 
race, afer. The first of these is an immigrant from Europe, 
the second from Asia, and the third was brought hither 
from Africa by representatives of var. europceus to be used 
as slaves." 



CHAPTER XIX 

THE LIFE CYCLE 

231. Birth, growth and development, and death. — Certain 
phenomena are familiar to ns as occurring inevitably in the 
life of every animal. Each individual is born in an imma- 
ture or young condition ; it grows (that is, it increases in 
size), and develops (that is, changes more or less in struc- 
ture), and dies. These phenomena occur in the succession 
of birth, growth and development, and death. But before 
any animal appears to us as an independent individual — 
that is, outside the body of the mother and outside of an 
egg (i. e., before birth or hatching, as we are accustomed to 
call such appearance) — it has already undergone a longer 
or shorter period of life. It has been a new living organ- 
ism hours or days or months, perhaps, before its appear- 
ance to us. This period of life has been passed inside an 
egg, or as an egg or in the egg stage, as it is variously 
termed. The life of an animal as a distinct organism be- 
gins in an egg. And the true life cycle of an organism is 
its life from egg through birth, growth and development, 
and maturity to the time it produces new organisms in 
the condition of eggs. The life cycle is from egg to egg. 
Birth and growth, two of the phenomena readily apparent 
to us in the life of every animal, are two phenomena in the 
true life cycle. Death is a third inevitable phenomenon in 
the life of each individual, but it is not a part of the cycle. 
It is something outside. 

232. Life cycle of simplest animals. — The simplest ani- 
mals have no true egg stage, nor perhaps have they any true 

254 



THE LIFE CYCLE 



255 



death. The new Amcebce are from their beginning like the 
full-grown Amoeba, except as regards size. And the old 
Amceba does not die, because its whole body continues to 
live, although in two parts — the two new Amoeba. The life 
cycle of the simplest animals includes birth (usually by 
simple fission of the body of the parent), growth, and some, 
but usually very little, development, and finally the repro- 
duction of new individuals, not by the formation of eggs, 
but by direct division of the body. 

233. The egg. — In our study of the multiplication of ani- 
mals (Chapter VI) we learned that it is the almost univer- 




Fig. 142.— Eggs of different animals showing variety in external appearance, a. egg 
of bird ; b, eggs of toad ; c, egg of fish ; d, egg of butterfly ; e, eggs of katydid 
on leaf ; /,egg-case of skate. 

sal rule among many-celled animals that each individual 
begins life as a single cell, which has been produced by the 



256 ANIMAL STUDIES 

fusion of two germ cells, a sperm cell from a male indi- 
vidual of the species and an egg cell from a female indi- 
vidual of the species. The single cell thus formed is called 
the fertilized egg cell, and its subsequent development 
results in the formation of a new individual of the same 
species with its parents. Now, in the development of this 
cell into a new animal, food is necessary, and sometimes a 
certain amount of warmth. So with the fertilized egg cell 
there is, in the case of all animals that lay eggs, a greater 
or less amount of food matter — food yolk, it is called — gath- 
ered about the germ cell, and both germ cell and food yolk 
are inclosed in a soft or hard wall. Thus is composed the 
egg as we know it. The hen's egg is as large as it is be- 
cause of the great amount of food yolk it contains. The 
egg of a fish as large as a hen is much smaller than the 
hen's egg ; it contains less food yolk. Eggs (Fig. 142) may 
vary also in their external appearance, because of the dif- 
ferent kinds of membrane or shells which may inclose and 
protect them. Thus the frog's eggs are inclosed in a thin 
membrane and imbedded in a soft, jelly-like substance ; 
the skate's egg has a tough, dark-brown leathery inclosing 
wall ; the spiral egg of the bull-head sharks is leathery and 
colored like the dark-olive seaweeds among which it lies ; 
and a bird's egg has a hard shell of carbonate of lime. But 
in each case there is the essential fertilized germ cell ; in 
this the eggs of hen and fish and butterfly and cray-fish and 
worm are alike, however much they may differ in size and 
external appearance. 

234. Embryonic and post-embryonic development. — Some 
animals do not lay eggs, that is they do not deposit the fer- 
tilized egg cell outside of the body, but allow the develop- 
ment of the new individual to go on inside the body of the 
mother for a longer or shorter period. The mammals and 
some other animals have this habit. When such an ani- 
mal issues from the body of the mother, it is said to be 
born. When the developing animal issues from an egg 



THE LIFE CYCLE 



257 



which has been deposited outside the body of the mother, 
it is said to hatch. The animal at birth or at time of hatch- 
ing is not yet fully developed. Only part of its development 
or period of immaturity is passed within the egg or within 
the body of the mother. That part of its life thus passed 
within the egg or mother's body is called the embryonic life 
or embryonic stages of development ; while that period of 
development or immaturity from the time of birth or hatch- 
ing until maturity is reached is called the post-embryonic 
life or post-embryonic stages of development. 

235. First stages in development. — The embryonic develop- 
ment is from the beginning up to a certain point practically 
identical for all many-celled animals — that is, there are cer- 




Fig. 143.— First stages in embryonic development of the pond snail (Lymnceus). a t 
egg cell ; b, first cleavage ; c, second cleavage ; d, third cleavage ; e, after numer- 
ous cleavages ; /, blastula (in section) ; g, gastrula, just forming (in section) ; 
k, gastrula, completed (in section).— After Rabl. 

tain principal or constant characteristics of the beginning 
development which are present in the development of all 
many-celled animals. The first stage or phenomenon of 
development is the simple fission of the germ cell into 
halves (Fig. 143, V). These two daughter cells next divide so 
that there are four cells (Fig. 143, c) ; each of these divides, 
and this division is repeated until a greater or lesser num- 



258 ANIMAL STUDIES 

ber (varying with the various species or groups of animals) 
of cells is produced (Fig. 143, d). The phenomenon of re- 
peated division of the germ cell, and usually the surround- 
ing yolk, is called cleavage, and this cleavage is the first 
stage of development in the case of all many-celled animals. 
The first division of the germ cell produces usually two equal 
cells, but in some of the later divisions the new cells formed 
may not be equal. In some animals all the cleavage cells are 
of equal size ; in some there are two sizes of cells. The germ 
or embryo animal consists now of a mass of few or many 
undifferentiated primitive cells lying together and usually 
forming a sphere (Fig. 143, e), or perhaps separated and scat- 
tered through the food yolk of the egg. The next stage of de- 
velopment is this : the cleavage cells arrange themselves so 
as to form a hollow sphere or ball, the cells lying side by side 
to form the outer circumferential wall of this hollow sphere 
(Fig. 143,/). This is called the Uastula or blastoderm stage 
of development, and the embryo itself is called the blastula 
or blastoderm. This stage also is common to all the many- 
celled animals. The next stage in embryonic development 
is formed by the bending inward of a part of the blasto- 
derm cell layer, as shown in Fig. 143, g. This bending in 
may produce a small depression or groove ; but whatever the 
shape or extent of the sunken-in part of the blastoderm, it 
results in distinguishing the blastoderm layer into two 
parts, a sunken-in portion called the endoblast and the 
other unmodified portion called the ectoblast. Endo- means 
" within," and the cells of the endoblast often push so far 
into the original blastoderm cavity as to come into contact 
with the cells of the ectoblast and thus obliterate this cavity 
(Fig. 143, Ji). This third well-marked stage in the embry- 
onic development is called the gastrula * stage, and it also 



* This gastrula stage is not always formed by a bending in or in- 
vagination of Hie blastoderm, but in some animals is formed by the 
splitting off or delamination of cells from a definite limited region of 



THE LIFE CYCLE 259 

occurs in the development of all or nearly all many-celled 
animals. 

236. Continuity of development. — In the case of a few of 
the simple many-celled animals the embryo hatches — that 
is, issues from the egg at the time of or very soon after 
reaching the gastrula stage. In the higher animals, how- 
ever, development goes on within the egg or within the 
body of the mother until the embryo becomes a complex 
body, composed of many various tissues and organs. Al- 
most all the development may take place within the egg, 




£1 

Fig. 144. — Honey-bee. a. adult worker ; b, young or larval worker. 

so that when the young animal hatches there is necessary 
little more than a rapid growth and increase of size to 
make it a fully developed, mature animal. This is the case 
with the birds : a chicken just hatched has most of the 
tissues and organs of a full-grown fowl, and is simply a 
little hen. But in the case of other animals the young 
hatches from the egg before it has reached such an ad- 
vanced stage of development ; a young star-fish or young 
crab or young honey-bee (Fig. 144) just hatched looks very 
different from its parent. It has yet a great deal of devel- 
opment to undergo before it reaches the structural condi- 
tion of a fully developed and fully grown star-fish or crab 
or bee. Thus the development of some animals is almost 

the blastoderm. Our knowledge of gastrulation and the gastrula stage 
is yet far from complete. 



260 ANIMAL STUDIES 

wholly embryonic development — that is, development with« 
in the egg or in the body of the mother — while the devel- 
opment of other animals is largely post-embryonic or larval 
development, as it is often called. There is no important 
difference between embryonic and post-embryonic develop- 
ment. The development is continuous from egg-cell to 
mature animal, and whether inside or outside of an egg it 
goes on regularly and uninterruptedly. 

237. Development after the gastrula stage. — The cells which 
compose the embryo in the cleavage stage and blastoderm 
stage, and even in the gastrula stage, are all similar ; there 
is little or no differentiation shown among them. But from 
the gastrula stage on development includes three important 
things : the gradual differentiation of cells into various 
kinds to form the various kinds of animal tissues ; the 
arrangement and grouping of these cells into organs and 
body parts ; and finally the developing of these organs 
and body parts into the special condition characteristic of 
the species of animal to which the developing individual 
belongs. From the primitive undifferentiated cells of the 
blastoderm, development leads to the special cell types of 
muscle tissue, of bone tissue, of nerve tissue ; and from the 
generalized condition of the embryo in its early stages de- 
velopment leads to the specialized condition of the body of 
the adult animal. Development is from the general to the 
special, as was said years ago by the first great student of 
development. 

238. Divergence of development. — A star-fish, a beetle, a 
dove, and a horse are all alike in their beginning — that is, 
the body of each is composed of a single cell, a single struc- 
tural unit. And they are all alike, or very much alike, 
through several stages of development ; the body of each 
is first a single cell, then a number of similar undifferen- 
tiated cells, and then a hollow sphere consisting of a single 
layer of similar undifferentiated cells. But soon in the 
course of development the embryos begin to differ, and as 



THE LIFE CYCLE 261 

the young animals get further and further along in the 
course of their development, they become more and more 
different until each finally reaches its fully developed ma- 
ture form, showing all the great structural differences be- 
tween the star-fish and the dove, the beetle and the horse. 
That is, all animals begin development alike, but gradually 
diverge from each other during the course of development. 
There are some extreme] y interesting and significant 
things about this divergence to which attention should be 
given. While all animals are alike structurally* at the 
Deginning of development, so far as we can see, they do not 
all differ at the time of the first divergence in development. 
This first divergence is only to be noted between two kinds 
of animals which belong to different great groups or classes. 
But two animals of different kinds, both belonging to some 
one great group, do not show differences until later in their 
development. This can best be understood by an example. 
All the butterflies and beetles and grasshoppers and flies 
belong to the great group of animals called Insecta, or in- 
sects. There are many different kinds of insects, and these 
kinds can be arranged in subordinate groups, such as the 
Diptera, or flies, the Lepidoptera, or butterflies and moths, 
and so on. But all have certain structural characteristics 
in common, so that they are comprised in one great group 
or class — the Insecta. Another great group of animals is 
known as the Vertebrata, or back-boned animals. The class 
Vertebrata includes the fishes, the batrachians, the reptiles, 
the birds, and the mammals, each composing a subordinate 
group, but all characterized by the possession of a back- 

* They are alike structurally, when we consider the cell as the unit 
of animal structure. That the egg cells of different animals may dif- 
fer in their fine or ultimate structure, seems certain. For each one of 
these egg cells is destined to become some one kind of animal, and no 
other ; each is, indeed, an individual in simplest, least developed con- 
dition of some one kind of animal, and we must believe that difference 
in kind of animals depends upon difference in structure in the egg itself. 



262 ANIMAL STUDIES 

bone, or, more accurately speaking, of a notochord, a back- 
bone-like structure. Now, an insect and a vertebrate di- 
verge very soon in their development from each other ; but 
two insects, such as a beetle and a honey-bee, or any two 
vertebrates, such as a frog and a pigeon, do not diverge 
from each other so soon. That is, all vertebrate animals 
diverge in one direction from the other great groups, but 
all the members of the great group keep together for some 
time longer. Then the subordinate groups of the Verte- 
brata, such as the fishes, the birds, and the others diverge, 
and still later the different kinds of animals in each of 
these groups diverge from each other. In the illustration 
(Fig. 145) on the opposite page will be seen pictures of the 
embryos of various vertebrate animals shown as they appear 
at different stages or times in the course of development. 
The embryos of a fish, a salamander, a tortoise, a bird, and 
a mammal, representing the five principal groups of the 
Vertebrata, are shown. In the upper row the embryos are 
in the earliest of all the stages figured, and they are very 
much alike. They show no obvious characteristics of 
fish or bird. Yet there are distinctive characteristics of 
the great class Vertebrata. Any of these embryos could 
readily be distinguished from an embryonic insect or worm 
or sea-urchin. In the second row there is beginning to be 
manifest a divergence among the different embryos, al- 
though it would still be a difficult matter to distinguish 
certainly which was the young fish and which the young 
salamander, or which the young tortoise and which the 
young bird. In the bottom row, showing the animals in a 
later stage of development, the divergence has proceeded 
so far that it is now plain which is a fish, which batrachian, 
which reptile, which bird, and which mammal. 

239. The laws or general facts of development. — That the 
course of development of any animal from its beginning to 
fully developed adult form is fixed and certain is readily 
seen. Every rabbit develops in the same way ; every grass- 




/7s/i 



in m 

\Sci/a m an tier 

Jprtoise Chick 

Fig. 145.— Different vertebrate animal in successive embryonic stages. I, first 
or earliest of the stages figured ; II, second of the stages ; III, third or 
latest of the stages. — After Haeckel. 



nr 



264 ANIMAL STUDIES 

hopper goes through the same developmental changes from 
single egg cell to the full-grown active hopper as every 
other grasshopper of the same kind — that is, development 
takes place according to certain natural laws, the laws of 
animal development. These laws may be roughly stated as 
follows : All many-celled animals begin life as a single cell, 
the fertilized egg cell ; each animal goes through a certain 
orderly series of developmental changes which, accom- 
panied by growth, leads the animal to change from single 
cell to the many-celled, complex form characteristic of the 
species to which the animal belongs ; this development is 
from simple to complex structural condition ; the develop- 
ment is the same for all individuals of one species. While 
all animals begin development similarly, the course of devel- 
opment in the different groups soon diverges, the diver- 
gence being of the nature of a branching, like that shown 
in the growth of a tree. In the free tips of the smallest 
branches we have represented the various species of ani- 
mals in their fully developed condition, all standing clearly 
apart from each other. But in tracing back the develop- 
ment of any kind of animal, we soon come to a point where 
it very much resembles or becomes apparently identical 
with some other kind of animal, and going further back we 
find it resembling other animals in their young condition, 
and so on until we come to that first stage of development, 
that trunk stage, where all animals are structurally alike. 
To be sure, any animal at any stage in its existence differs 
absolutely from any other kind of animal, in that it can 
develop into only its own kind of animal. There is some- 
thing inherent in each developing animal that gives it an 
identity of its own. Although in its young stages it may be 
hardly distinguishable from some other kind of animal in 
similar stages, it is sure to come out, when fully developed, 
an individual of the same kind as its parents were or are. 
The young fish and the young salamander in the upper row 
in Fig. 145 seem very much alike, but one embryo is sure to 



THE LIFE CYCLE 265 

develop into a fish and the other into a salamander. This 
certainty of an embryo to become an individual of a certain 
kind is called the law of heredity. 

240. The significance of the facts of development. — The 
significance of the developmental phenomena is a matter 
about which naturalists have yet very much to learn. It is 
believed, however, by practically all naturalists that many 
of the various stages in the development of an animal cor- 
respond to or repeat the structural condition of the ani- 
mal's ancestors. Naturalists believe that all backboned or 
vertebrate animals are related to each other through being 
descended from a common ancestor, the first or oldest 
backboned animal. In fact, it is because all these back- 
boned animals — the fishes, the batrachians, the reptiles, the 
birds, and the mammals — have descended from a common 
ancestor that they all have a backbone. It is believed that 
the descendants of the first backboned animal have in 
the course of many generations branched off little by little 
from the original type until there came to exist very real and 
obvious differences among the backboned animals — differ- 
ences which among the living backboned animals are familiar 
to all of us. The course of development of an individual ani- 
mal is believed by many naturalists to be a very rapid, and 
evidently much condensed and changed, recapitulation of 
the history which the species or kind of animal to which the 
developing individual belongs has passed through in the 
course of its descent through a long series of gradually chang- 
ing ancestors. If this is true, then we can readily under- 
stand why the fish and the salamander and tortoise and 
bird and rabbit are all so much alike in their earlier stages 
of development, and gradually come to differ more and 
more as they pass through later and later developmental 
stages. 

Some naturalists believe that the ontogenetic stages are 
not as significant in throwing light upon the evolutionary 
history of the species as just indicated. Some think that 
18 



266 ANIMAL STUDIES 

when the earlier stages of one species correspond pretty 
closely with the early stages of another, we have a good 
basis for making np our minds about relationship between 
the two species. But it is certainly not obvious why we 
should have a similarity among the younger stages of dif- 
ferent animals and no correspondence among the older 
stages of more recent animals with the younger stages of 
more ancient ones. But on the other hand it is certainly 
true that a too specific application of the broad generaliza- 
tion that ontogeny repeats phylogeny has led to numerous 
errors of interpreting genealogic relationship. 

241. Metamorphosis. — While a young robin when it 
hatches from the egg or a young kitten at birth resembles its 
parents, a young star-fish or a young crab or a young butter- 
fly when hatched does not at all resemble its parents. And 
while the young robin after hatching becomes a fully grown 
robin simply by growing larger and undergoing compara- 
tively slight developmental changes, the young star-fish or 
young butterfly not only grows larger, but undergoes some 
very striking developmental changes; the body changes 
very much in appearance. Marked changes in the body of 
an animal during post-embryonic or larval development 
constitute what is called metamorphic development, or the 
animal is said to undergo or to show metamorphosis in its 
development. Metamorphosis is one of the most interest- 
ing features in the life history or development of animals, 
and it can be, at least as far as its external aspects are con- 
cerned, very readily observed and studied. 

242. Metamorphosis among insects. — All the butterflies 
and moths show metamorphosis in their development. So do 
many other insects, as the ants, bees, and wasps, and all the 
flies and beetles. On the other hand, many insects do not 
show metamorphosis, but, like the birds, are hatched from 
the egg in a condition plainly resembling the parents. A 
grasshopper (Fig. 146) is a convenient example of an insect 
without metamorphosis, or rather, as there are, after all, 



THE LIFE CYCLE 



267 



a few easily perceived changes in its post-embryonic devel- 
opment, of an insect with an "incomplete metamorpho- 
sis." The eggs of grasshoppers are laid in little packets 
of several score half an inch below the surface of the 
ground. When the young grasshopper hatches from the 
egg it is of course very small, but it is plainly recognizable 
as a grasshopper. But in one important character it dif- 
fers from the adult, and that is in its lack of wings. The 
adult grasshopper has two pairs of wings ; the just hatched 
young or larval grasshopper has no wings at all. The 
young grasshopper feeds voraciously and grows rapidly. 




Fig. 146.— Post-embryonic development (incomplete metamorphosis) of the Kocky 
Mountain locust {Melanoplus spretus). a, b, c, d, e, and /, successive develop- 
mental stages from just hatched to adult individual.— After Emerton. 



In a few days it molts, or casts its outer skin (not the 
true skin, but a thin, firm covering or outer body wall com- 
posed of a substance called chitin, which is secreted by the 
cells of the true skin). In this second larval stage there 
can be seen the rudiments of four wings, in the condition 
of tiny wing pads on the back of the middle part of the 
body (the thorax). Soon the chitinous body covering is 
shed again, and after this molt the wing pads are mark- 
edly larger than before. Still another molt occurs, with 
another increase in size of the developing wings, and after 
a fifth and last molt the wings are fully developed, and 



268 ANIMAL STUDIES 

the grasshopper is no longer in a larval or immature condi- 
tion, but is full grown and adult. 

For example of complete metamorj^hosis among insects 
wc may choose a butterfly, the large red-brown butterfly 




Fig. 147.— Metamorphosis of monarch butterfly (Anosia plexippus). a, egg ; b, larva ; 
c, pupa ; d, imago or adult. 

common in the United States and called the monarch or 
milkweed butterfly {Anosia plexippus). The eggs (Fig. 
147, a) of this butterfly are laid on the leaves of various kinds 
of milkweed (Asclepias). The larval butterfly or butterfly 
larva or caterpillar (as the first young stage of the butter- 



THE LIFE CYCLE 



269 



flies and moths is usually called), which hatches from the 
egg in three or four days, is a creature bearing little or 
no resemblance to the beautiful winged adult. The larva 
is worm-like, and instead of having three pairs of legs 
like the butterfly it has eight pairs; it has biting jaws 
in its mouth with which it nips off bits of the green milk- 
weed leaves, instead of having a long, slender, sucking 
proboscis for drinking flower nectar as the butterfly has. 
The body of the crawl- 
ing worm-like larva 
(Fig. 147, 1) is greenish 
yellow in color, with 
broad rings or bands of 
shining black. It has 
no wings, of course. It 
eats voraciously, grows 
rapidly and molts. But 
after the molting there 
is no appearance of 
rudimentary wings ; it 
is simply a larger worm- 
like larva. It continues 
to feed and grow, molt- 
ing several times, until 
after the fourth molt it 
appears no longer as an 
active, crawling, feed- 
ing, worm-like larva, but as a quiescent, non-feeding pupa 
or chrysalis (Fig. 147, c). The immature butterfly is now 
greatly contracted, and the outer chitinous wall is very 
thick and firm. It is bright green in color with golden dots. 
It is fastened by one end to a leaf of the milkweed, where 
it hangs immovable for from a few days to two weeks. 
Finally, the chitin wall of the chrysalis splits, and there 
issues the full-fledged, great, four-winged, red-brown butter- 
fly (Fig. 147, d). Truly this is a metamorphosis, and a start- 




Fig. 14S. — Metamorphosis of mosquito ( Culex). 
a, larva ; b, pupa. 



270 



ANIMAL STUDIES 



ling one. Bnt we know that development in other animals 
is a gradual and continuous process, and so it is in the 

case of the butterfly. 
The gradual chang- 
ing is masked by the 
outer covering of the 
body in both larva 
and pupa. It is only 
at each molting or 
throwing off of this 
unchanging, unyield- 
ing chitin armor that 
we perceive how far 
this change has gone. 
The longest time of 
concealment is that 
during the pupal or 
chrysalis stage, and 
the results of the 
changing or develop- 
ment when finally re- 
vealed by the split- 
ting of the pupal 
case are hence the 
most striking. 

243. Metamorphosis among other animals. — Many other 
animals, besides insects and frogs and toads, undergo meta- 
morphosis. The just-hatched sea-urchin does not resemble 
a fully developed sea-urchin at all. It is a minute worm- 
like creature, provided with cilia or vibratile hairs, by means 
of which it swims freely about. It changes next into a curi- 
ous boot-jack shaped body called the pluteus stage (Fig. 150). 
In the pluteus a skeleton of lime is formed, and the final 
true sea-urchin body begins to appear inside the pluteus, 
developing and growing by using up the body substance of 
the pluteus. Star-fishes, which are closely related to sea- 



, 




J 








1 




Hgv. * 


J 












i 




i 



Fig. 149. — Larva of a butterfly just changing into 
pupa (making last larval molt). Photograph 
from nature. 



THE LIFE CYCLE 



271 



urchins, show a similar metamorphosis, except that there is 
no pluteus stage, the true star-fish-shaped body forming, 
within and at the expense of the first larval stage, the ciliated 
free-swimming stage. 

A young crab just issued from the egg (Fig. 151) is a 
very different appearing creature from the adult or fully 
developed crab. The body of the crab in its first larval 
stage is composed of a short, globular portion, furnished with 
conspicuous long spines and a relatively long, jointed tail. 



iiWikV<J""f*.tlAs 




Fim. 150.— Metamorphosis of sea-urchin. Upper figure the adult, lower ngure the 
pluteus larva. 



This is called the zoea stage. The zoea changes into a stage 
called the megalops, which has many characteristics of the 
adult crab condition, but differs especially from it in the 
possession of a long, segmented tail, and in having the front 



272 



ANIMAL STUDIES 



half of the body longer than wide. The crab in the megalops 
stage looks very much like a tiny lobster or shrimp. The 
tail soon disappears and the body widens, and the final stage 
is reached. 

Interesting examples of metamorphosis occur in nearly 
all species of the animal kingdom, those mentioned being, 




Fig. 151.— Metamorphosis of the crab. «, the zo&i sta 

c, the adult. 



; b. the megalops; 



perhaps, the most conspicuous. In many families of fishes 
the changes which take place in the course of the life cycle 
are almost as great as in the case of the insect or the toad. In 
the lady-fish {Albula vulpes) the very young are ribbon-like in 
form, with small heads and very loose texture of the tissues, 
the body substance being jelly-like and transparent. As the 
fish grows older the body becomes more compact, and there- 
fore shorter and slimmer. After shrinking to the texture of 
an ordinary fish, its growth in size begins normally, although 



THE LIFE CYCLE 



273 



it has steadily increased in actual weight. Many herring, 
eels, and other soft-bodied fishes pass through stages simi- 
lar to those seen in the lady-fish. Another type of devel- 
opment is illustrated in the sword-fish. The young has a 
bony head, bristling with spines. As it grows older the 
spines disappear, the skin grows smoother, and, finally, the 
bones of the upper jaw grow together, forming a prolonged 
sword, the teeth are lost and, the fins become greatly modi- 
fied. Fig. 152 shows three of these stages of growth. The 





Pig. 152.— Three stages in the development of the sword-fish (Xiphic 
a, very young ; b, older ; c, adult.— Partly after Ltjtken. 



gladius). 



flounder or flat-fish (Fig. 152) when full grown lies flat on 
one side when swimming or when resting in the sand on 
the bottom of the sea. The eyes are both on the upper 
side of the body, and the lower side is blind and colorless. 
When the flounder is hatched it is a transparent, fish, broad 
and flat, swimming vertically in the water, with an eye on 
each side. As its development (Fig. 153) goes on it rests 
itself obliquely on the bottom, the eye of the lower side 
turns upward, and as growth proceeds it passes gradually ( 



274: 



ANIMAL STUDIES 



around the forehead, its socket moving with it, until both 
eyes and sockets are transferred by twisting of the skull to 




Fig. 153.— The wide eyed flounder (Platophrys lunatus). Adult, showing both eyes on 
upper side of head. 

the upper side. In some related forms or soles the small 
eye passes through the head and not around it, appearing 
finally in the same socket with the other eye. 

Thus in almost all the great groups of animals we find 
certain kinds which show metamorphosis in their post- 
embryonic development. But metamorphosis is simply 
development; its striking and extraordinary features are 
usually due to the fact that the orderly, gradual course of 
the development is revealed to us only occasionally, with 
the result of giving the impression that the development is 
proceeding by leaps and bounds from one strange stage to 




Fig. 154.— Development of a flounder (after Emert). The eyes in the young flounder 
are arranged normally, one on each side of head. 

another. If metamorphosis is carefully studied it loses its 
aspect of marvel, although never its great interest. 



THE LIFE CYCLE 



275 



244. Duration of life. — After an animal has completed its 
development it has but one thing to do to complete its life 
cycle, and that is the production of offspring. When it 
has laid eggs or given birth to young, it has insured the 
beginning of a new life cycle. Does it now die ? Is the 
business of its life accomplished ? There are many animals 
which die immediately or very soon after laying eggs. The 
May-flies — ephemeral insects which issue as winged adults 
from ponds or lakes in which 
they have spent from one to 
three years as aquatic crawl- 
ing or swimming larvae, flutter 
about for an evening, mate, 
drop their packets of fertil- 
ized eggs into the water, and 
die before the sunrise — are 
extreme examples of the nu- 
merous kinds of animals 
whose adult life lasts only long 
enough for mating and egg- 
laying. But elephants live for 
two hundred years. Whales 
probably live longer. A horse ^^Pf" 

t . t jii-i n Fig. 155. — Metamorphosis of a barnacle 

lives about thirty years, and so {Lepas) a> larva . b adult 

may a cat or toad. A sea- 
anemone, which was kept in an aquarium, lived sixty-six 
years. Cray-fishes may live twenty years. A queen bee 
was kept in captivity for fifteen years. Most birds have 
long lives — the small song birds from eight to eighteen 
years, and the great eagles and vultures up to a hundred 
years or more. On the other hand, among all the thou- 
sands of species of insects, the individuals of very few in- 
deed live more than a year ; the adult life of most insects 
being but a few days or weeks, or at best months. Even 
among the higher animals, some are very short-lived. 
In Japan is a small fish (Solaux) which probably lives 




276 ANIMAL STUDIES 

but a year, ascending the rivers in numbers when young in 
the spring, the whole mass of individuals dying in the fall 
after spawning. 

Xaturalists have sought to discover the reason for these 
extraordinary differences in the duration of life of different 
animals, and while it can not be said that the reason or 
reasons are wholly known, yet the probability is strong that 
the duration of life is closely connected with, or dependent 
upon, the conditions attending the production of offspring. 
It is not sufficient, as we have learned from our study of 
the multiplication of animals (Chapter VI), that an adult 
animal shall produce simply a single new individual of its 
kind, or even only a few. It must produce many, or if it 
produces comparatively few it must devote great care to 
the rearing of these few, if the perpetuation of the species 
is to be insured. Now, almost all long-lived animals are 
species which produce but few offspring at a time, and 
reproduce only at long intervals, while most short-lived ani- 
mals produce a great many eggs,' and these all at one time. 
Birds are long-lived animals; as we know, most of them 
lay eggs but once a year, and lay only a few eggs each time. 
Many of the sea birds which swarm in countless numbers 
on the rocky ocean islets and great sea cliffs lay only a 
single egg once each year. And these birds, the guillemots 
and murres and auks, are especially long-lived. Insects, on 
the contrary, usually produce many eggs, and all of them 
in a short time. The May-fly, with its one evening's lifetime, 
lets fall from its body two packets of eggs and then dies. 
Thus the shortening of the period of reproduction with the 
production of a great many offspring seem to be always 
associated with a short adult lifetime ; while a long period 
of reproduction with the production of few offspring at a 
time and care of the offspring are associated with a long 
adult lifetime. 

There seems also to be some relation between the size 
of animals and the length of life. As a general rule, 



THE LIFE CYCLE 277 

large animals are long-lived and small animals have short 
lives. 

245. The number of young. — There is great variation in the 
number of young produced by different species of animals. 
Among the animals we know familiarly, as the mammals, 
which give birth to young alive, and the birds, which lay 
eggs, it is the general rule that but few young are pro- 
duced at a time, and the young are born or eggs are laid 
only once or perhaps a few times in a year. The robin lays 
five or six eggs once or twice a year; a cow may produce 
a calf each year. Eabbits and pigeons are more prolific, 
each having several broods a year. But when we observe 
the multiplication of some of the animals whose .habits are 
not so familiar to us, we find that the production of so few 
young is the exceptional and not the usual habit. A lob- 
ster lays ten thousand eggs at a time; a queen bee lays 
about five million eggs in her life of four or five years. A 
female white ant, which after it is full grown does nothing 
but lie in a cell and lay eggs, produces eighty thousand 
eggs a day steadily for several months. A large codfish 
was found on dissection to contain about eight million 



If we search for some reason for this great difference in 
fertility among different animals, we may find a promis- 
ing clew by attending to the duration of life of animals, 
and to the amount of care for the young exercised by the 
parents. We find it to be the general rule that animals 
which live many years, and which take care of their young, 
produce but few young; while animals which live but a 
short time, and which do not care for their young, are very 
prolific. The codfish produces its millions of eggs ; thou- 
sands are eaten by sculpins and other predatory fishes be- 
fore they are hatched, and other thousands of the defense- 
less young fish are eaten long before attaining maturity. 
Of the great number produced by the parent, a few only 
reach maturity and produce new young. But the eggs of the 



278 ANIMAL STUDIES 

robin are hatched and protected, and the helpless fledglings 
are fed and cared for until able to cope with their natural 
enemies. In the next year another brood is carefully reared, 
and so on for the few years of the robin's life. 

Under normal conditions in any given locality the num- 
ber of individuals of a certain species of animal remains 
about the same. The fish which produces tens of thousands 
of eggs and the bird which reproduces half a dozen eggs a 
year maintain equally well their numbers. In one case a 
few survive of many born ; in the other many (relatively) 
survive of the few born ; in both cases the species is effect- 
ively maintained. In general, no agency for the perpetua- 
tion of the species is so effective as that of care for the 
young. 

246. Death. — At the end comes death. After the animal 
has completed its life cycle, after it has done its share toward 
insuring the perpetuation of its species, it dies. It may 
meet a violent death, may be killed by accident or by ene- 
mies, before the life cycle is completed. And this is the 
fate of the vast majority of animals which are born or 
hatched. Or death may come before the time for birth or 
hatching. Of the millions of eggs laid by a fish, each egg 
a new fish in simplest stage of development, how many or 
rather how few come to maturity, how few complete the 
cycle of life ! 

Of death we know the essential meaning. Life ceases 
and can never be renewed in the body of the dead animal. 
It is important that we include the words " can never be 
renewed," for to say simply that " life ceases," that is, that 
the performance of the life processes or functions ceases, 
is not really death. It is easy to distinguish in most cases 
between life and death, between a live animal and a dead 
one, yet there are cases of apparent death or a semblance of 
death which are very puzzling. The test of life is usually 
taken to be the performance of life functions, the assimila- 
tion of food and excretion of waste, the breathing in of oxy- 



THE LIFE CYCLE 279 

gen, and breathing out of carbonic-acid gas, movement, 
feeling, etc. But some animals can actually suspend all 
of these functions, or at least reduce them to such a mini- 
mum that they can not be perceived by the strictest exami- 
nation, and yet not be dead. That is, they can renew 
again the performance of the life processes. Bears and 
some other animals, among them many insects, spend the 
winter in a state of death-like sleep. Perhaps it is but sleep ; 
and yet hibernating insects can be frozen solid and remain 
frozen for weeks and months, and still retain the power of 
actively living again in the following spring. Even more 
remarkable is the case of certain minute animals called Ro- 
tatoria and of others called Tardigrada, or bear-animalcules. 
These bear-animalcules live in water. If the water dries 
up, the animalcules dry up too.; they shrivel up into form- 
less little masses and become desiccated. They are thus 
simply dried-up bits of organic matter; they are organic 
dust. Now, if after a long time — years even — one of these 
organic dust particles, one of these dried-up bear-animal- 
cules is put into water, a strange thing happens. The body 
swells and stretches out, the skin becomes smooth instead 
of all wrinkled and folded, and the legs appear in normal 
shape. The body is again as it was years before, and after 
a quarter of an hour to several hours (depending on the 
length of time the animal has lain dormant and dried) slow 
movements of the body parts begin, and soon the animal- 
cule crawls about, begins again its life where it had been 
interrupted. Various other small animals, such as vinegar 
eels and certain Protozoa, show similar powers. Certainly 
here is an interesting problem in life and death. 

When death comes to one of the animals with which 
we are familiar, we are accustomed to think of its coming 
to the whole body at some exact moment of time. As we 
stand beside a pet which has been fatally injured, we wait 
until suddenly we say, " It is dead." As a matter of fact, 
it is difficult to say when death occurs. Long after the 



280 ANIMAL STUDIES 

heart ceases to beat, other organs of the body are alive — 
that is, are able to perform their special functions. The 
muscles can contract for minutes or hours (for a short time 
in warm-blooded, for a long time in cold-blooded animals) 
after the animal ceases to breathe and its heart to beat. 
Even longer live certain cells of the body, epecially the 
amoeboid white blood-corpuscles. These cells, very like 
the Amoeba in character, live for days after the animai is, 
as we say, dead. The cells which line the tracheal tube 
leading to the lungs bear cilia or fine hairs which they 
wave back and forth. They continue this movement for 
days after the heart has ceased beating. Among cold- 
blooded animals, like snakes and turtles, complete cessa- 
tion of life functions comes very slowly, even after the 
body has been literally cut to pieces. 

Thus it is essential in defining death to speak of a 
complete and permanent cessation of the performance of 
the life processes. 



CHAPTEE XX 

THE CROWD OF ANIMALS AND THE STRUGGLE FOR 
EXISTENCE 

247. The crowd of animals. — All animals feed upon living 
organisms, or on their dead bodies. Hence each animal 
throughout its life is busy with the destruction of other 
organisms, or with their removal after death. If those 
creatures upon which others feed are to hold their own, there 
must be enough born or developed to make good the drain 
upon their numbers. If the plants did not fill up their 
ranks and make good their losses, the animals that feed 
on them would perish. If the plant-eating animals were 
destroyed, the flesh-eating animals would in turn disappear. 
But, fortunately, there is a vast excess in the process of 
reproduction. More plants sprout than can find room to 
grow. More animals are born than can possibly survive. 
The process of increase among animals is correctly spoken 
of as multiplication. Each species tends to increase in 
geometric ratio, but as it multiplies its members it finds 
the world already crowded with other species doing the 
same thing. A single pair of any species whatsoever, if not 
restrained by adverse conditions, would soon increase to 
such an extent as to fill the whole world with its progeny. 
An annual plant producing two seeds only would have 
1,048,576 descendants at the end of twenty-one years, if 
each seed sprouted and matured. The ratio of increase is 
therefore a matter of minor importance. It is the ratio of 
net increase above loss which determines the fate of a spe- 
cies. Those species increase in numbers whose gain exceeds 
19 ' 281 



282 ANIMAL STUDIES 

the death rate, and those which " live beyond their means " 
must sooner or later disappear. One of the most abundant 
of birds is the fulmar petrel, which lays out one egg yearly. 
It has but few enemies, and this low rate of increase suf- 
fices to cover the seas within its range with petrels. 

It is difficult to realize the inordinate numbers in which 
each species would exist were it not for the checks produced 
by the presence of other animals. Certain Protozoa at their 
normal rate of increase, if none were devoured or destroyed, 
might fill the entire ocean in about a week. The conger- 
eel lays, it is said, 15,000,000 eggs. If each egg grew 
up to maturity and reproduced itself in the same way in 
less than ten years the sea would be solidly full of conger- 
eels. If the eggs of a common house-fly should develop, and 
each of its progeny should find the food and temperature it 
needed, with no loss and no destruction, the people of a city in 
which this might happen could not get away soon enough to 
escape suffocation from a plague of flies. Whenever any in- 
sect is able to develop a large percentage of the eggs laid, it 
becomes at once a plague. Thus originate plagues of grass- 
hoppers, locusts, and caterpillars. But the crowd of life is 
such that no great danger exists. The scavenger destroys 
the decaying flesh where the fly would lay its eggs. Minute 
creatures, insects, bacteria, Protozoa are parasitic within 
the larva and kill it. Millions of flies perish for want of 
food. Millions more are destroyed by insectivorous birds, 
and millions are slain by parasites. The final result is that 
from year to year the number of flies does not increase. 
Linnaeus once said that " three flies would devour a dead 
horse as quickly as a lion." Equally soon would it be de- 
voured by three bacteria, for the decay of the horse is due 
to the decomposition of its flesh by these microscopic plants 
which feed upon it. " Even slow-breeding man," says Dar- 
win, " has doubled in twenty-five years. At this rate in less 
than a thousand years there would literally not be standing 
room for his progeny. The elephant is reckoned the slow- 



THE STRUGGLE FOR EXISTENCE 283 

est breeder of all known animals. It begins breeding when 
thirty years old and goes on breeding until ninety years 
old, bringing forth six young in the interval, and surviving 
till a hundred years old. If this be so, after about eight, 
hundred years there would be 19,000,000 elephants alive, 
descended from the first pair." A few years more of the 
unchecked multiplication of the elephant and every foot of 
land on the earth would be covered by them. 

Yet the number of elephants does not increase. In gen- 
eral, the numbers of every species of animal in the state of 
Nature remain about stationary. Under the influence of 
man most of them slowly diminish. There are about as 
many squirrels in the forest one year as another, about as 
many butterflies in the field, about as many frogs in the 
pond. Wolves, bears, deer, wild ducks, singing birds, fishes, 
tend to grow fewer and fewer in inhabited regions, because 
the losses from the hand of man are added to the losses in 
the state of Nature. 

It has been shown that at the normal rate in increase of 
English sparrows, if none were to die save of old age, it 
would take but twenty years to give one sparrow to everv 
square inch in the State of Indiana. Such an increase is 
actually impossible, for more than a hundred othei species 
of similar birds are disputing the same territory with the 
power of increase at a similar rate. There can not be food 
and space for all. With such conditions a struggle is set 
up between sparrow and sparrow, between sparrow and 
other birds, and between sparrow and the conditions of life. 
Such a conflict is known as the struggle for existence. 

248. The struggle for existence. — The struggle for exist- 
ence is threefold: (a) among individuals of one species, 
as sparrow and sparrow ; (b) between individuals of differ- 
ent species, as sparrow with bluebird or robin ; and (c) with 
the conditions of life, as the effort of the sparrow to keep 
warm in winter and to find water in summer. All three 
forms of this struggle are constantly operative and with 



284 ANIMAL STUDIES 

every species. In some regions the one phase may be more 
destructive, in others another. Where the conditions of 
life are most easy, as in the tropics, the struggle of species 
with species, of individual with individual, is the most 
severe. 

Xo living being can escape from any of these three 
phases of the struggle for existence. For reasons which we 
shall see later, it is not well that any should escape, for t; the 
sheltered life," the life withdrawn from the stress of effort, 
brings the tendency to degeneration. 

Because of the destruction resulting from the struggle 
for existence, more of every species are born than can 
possibly find space or food to mature. The majority fail 
to reach their full growth because, for one reason or an- 
other, they can not do so. All live who can. Each strives 
to feed itself, to save its own life, to protect its young. 
But with all their efforts only a portion of each species 
succeed. 

240. Selection by Nature. —But the destruction in Nature 
is not indiscriminate. In the long run those least fitted to 
resist attack are the first to perish. It is the slowest ani- 
mal which is soonest overtaken by those which feed upon 
it. It is the weakest which is crowded away from the feed- 
ing-place by its associates. It is the least adapted which is 
first destroyed by extremes of heat and cold. Just as a 
farmer improves his herd of cattle by destroying his weak- 
est or roughest calves, reserving the strong and fit for par- 
entage, so, on an inconceivably large scale, the forces of 
Nature are at work purifying, strengthening, and fitting to 
their surroundings the various species of animals. This 
process has been called natural selection, or the survival of 
the fittest. But by fittest in this sense we mean only best 
adapted to the surroundings, for this process, like others in 
Nature, has itself no necessarily moral element. The song- 
bird becomes through this process more fit for the song-bird 
life, the hawk becomes more capable of killing and tear- 



THE STRUGGLE FOR EXISTENCE 285 

ing, and the woodpecker better fitted to extract grubs from 
the tree. 

In the struggle of species with species one may gain a 
little one year and another the next, the numbers of each 
species fluctuating a little with varying circumstances, but 
after a time, unless disturbed by the hand of man, a point 
will be reached when the loss will almost exactly balance 
the increase. This produces a condition of apparent equi- 
librium. The equilibrium is broken when any individual or 
group of individuals becomes capable of doing something 
more than hold its own in the struggle for existence. 

When the conditions of life become adverse to the exist- 
ence of a species it has three alternatives, or, better, one of 
three things happens, namely, migration, adaptation, extinc- 
tion. The migration of birds and some other animals is a 
systematic changing of environment when conditions are 
unfavorable to life. When the snow and ice come, the fur- 
seal forsakes the islands on which it breeds, and which are 
its real home, and spends the rest of the year in the open 
sea, returning at the close of winter. Some other animals 
migrate irregularly, removing from place to place as condi- 
tions become severe or undesirable. The Eocky Mountain 
locusts, which breed on the great plateau along the eastern 
base of the Eocky Mountains, sometimes increase so rapidly 
in numbers that they can not find enough food in the scanty 
vegetation of this region. Then great hosts of them fly 
high into the air until they meet an air current moving 
toward the southeast. The locusts are borne by this cur- 
rent or wind hundreds of miles, until, when they come to 
the great grain-growing Mississippi Valley, they descend 
and feed to their hearts' content, and to the dismay of the 
Nebraska and Kansas farmer. These great forced migra- 
tions used to occur only too often, but none has taken place 
since 1878, and it is probable that none will ever occur 
again. With the settlement of the Eocky Mountain plateau 
by farmers, food is plenty at home. And the constant fight' 



286 ANIMAL STUDIES 

ing of the locusts by the farmers, by plowing up their eggs, 
and crushing and burning the young hoppers, keeps down 
their numbers. 

Another animal of interesting migratory habits is the 
lemming, a mouse-like animal nearly as large as a rat, which 
lives in the arctic regions. At intervals varying from five 
to twenty years the cultivated lands of Xorway and Sweden, 
where the lemming is ordinarily unknown, are overrun by 
vast numbers of these little animals. They come as an 
army, steadily and slowly advancing, always in the same 
direction, and " regardless of all obstacles, swimming across 
streams and even lakes of several miles in breadth, and 
committing considerable devastation on their line of march 
by the quantity of food they consume. In their turn they 
are pursued and harassed by crowds of beasts and birds of 
prey, as bears, wolves, foxes, dogs, wild cats, stoats, weasels, 
eagles, hawks, and owls, and never spared by man ; even 
the domestic animals not usually predaceous, as cattle, 
foals, and reindeer, are said to join in the destruction, 
stamping them to the ground with their feet and even eat- 
ing their bodies. Xumbers also die from disease apparently 
produced from overcrowding. Xone ever return by the 
course by which they came, and the onward march of the 
survivors never ceases until they reach the sea, into which 
they plunge, and swimming onward in the same direction 
as before perish in the waves." One of these great migra-" 
tions lasts for from one to three years. But it always ends 
in the total destruction of the migrating army. But the 
migration may be of advantage to the lemmings which re- 
main in the original breeding grounds, leaving them with 
enough food, so that, on the whole, the migration results in 
gain to the species. 

But most animals can not migrate to their betterment, 
tn that case the only alternatives are adaptation or destruc- 
tion. Some individuals by the possession of slight advan- 
tageous variations of structure are able to meet the new 



THE STRUGGLE FOR EXISTENCE 287 

demands and survive, the rest die. The survivors produce 
young similarly advantageously different from the general 
type, and the adaptation increases with successive genera- 
tions. 

250. Adjustment to surroundings a result of natural selec- 
tion.— To such causes as these we must ascribe the nice 
adjustment of each species to its surroundings. If a species 
or a group of individuals can not adapt itself to its environ- 
ment, it will be crowded out by others that can do so. The 
former will disappear entirely from the earth, or else will be 
limited to surroundings with which it comes into perfect 
adjustment. A partial adjustment must with time become 
a complete one, for the individuals not adapted will be 
exterminated in the struggle for life. In this regard very 
small variations may lead to great results. A side issue 
apparently of little consequence may determine the fate of 
a species. Any advantage, no matter how small, will turn 
the scale of life in favor of its possessor and his progeny. 
"Battle within battle," says a famous naturalist, "must be 
continually recurring, with varying success. Yet in the 
long run the forces are so nicely balanced that the face of 
Nature remains for a long time uniform, though assuredly 
the merest trifle would give the victory to one organic being 
over another." 

251. Artificial selection. — It has been long known that the 
nature of a herd or race of animals can be materially altered 
by a conscious selection on the part of man of these indi- 
viduals which are to become parents. To " weed out " a 
herd artificially is to improve its blood. To select for re- 
production the swiftest horses, the best milk cows, the most 
intelligent dogs, is to raise the standard of the herd or 
race in each of these respects by the simple action of hered- 
ity. Artificial selection has been called the "magician's 
wand," by which the breeder can summon up whatever 
animal form he will. If the parentage is chosen to a defi- 
nite end, the process of heredity will develop the form 



288 ANIMAL STUDIES 

desired by a force as unchanging as that by which a stream 
turns a mill. 

From the wild animals about him man has developed 
the domestic animals which he finds useful. The dog 
which man trains to care for his sheep is developed by 
selection from the most tractable progeny of the wolf which 
once devoured his flocks. By the process of artificial selec- 
tion those individuals that are not useful to man or pleas- 
ing to his fancy have been destroyed, and those which con- 
tribute to his pleasure or welfare have been preserved and 
allowed to reproduce their kind. The various fancy breeds 
of pigeons — the carriers, pouters, tumblers, ruff-necks, and 
fan-tails — are all the descendants of the wild dove of Eu- 
rope (Columba livia). These breeds or races or varieties 
have been produced by artificial selection. So it is with 
the various breeds of cattle and of hogs and of horses 
and dogs. 

In this artificial selection new variations are more rap- 
idly produced than in Nature by means of intercrossing 
different races, and by a more rapid weeding out of un- 
favorable — that is, of undesirable — variations. The rapid 
production of variations and the careful preservation of 
the desirable ones and rigid destruction of undesirable 
ones are the means by which many races of domestic ani- 
mals are produced. This is artificial selection. 

252. Dependence of species on species.— There was intro- 
duced into California from Australia, on young orange trees, 
a few years ago, an insect pest called the cottony cushion 
scale {Iccrya purchasi). This pest increased in numbers 
with extraordinary rapidity, and in four or five years threat- 
ened to destroy completely the great orange orchards of 
California. Artificial remedies were of little avail. Finally, 
an entomologist was sent to Australia to find out if this 
scale insect had not some speeial natural enemy in its 
native country. It was found that in Australia a certain 
species of lady-bird beetle attacked and fed on the cottony 



THE STRUGGLE FOR EXISTENCE 289 

cushion scales and kept them in check. Some of these 
lady-birds ( Vedalia cardinalis) were brought to California 
and released in a scale-infested orchard. The lady-birds, 
having plenty of food, thrived and produced many young. 
Soon the lady-birds were in such numbers that numbers of 
them could be distributed to other orchards. In two or 
three years the Vedalias had become so numerous and 
widely distributed that the cottony cushion scales began to 
diminish perceptibly, and soon the pest was nearly wiped 
out. But with the disappearance of the scales came also a 
disappearance of the lady-birds, and it was then discovered 
that the Vedalias fed only on cottony cushion scales and 
could not live where the scales were not. So now, in order 
to have a stock of Vedalias on hand in California it is neces- 
sary to keep protected some colonies of the cottony cushion 
scale to serve as food. Of course, with the disappearance 
of the predaceous lady-birds the scale began to increase 
again in various parts of the State, but with the sending of 
Vedalias to these localities the scale was again crushed. 
How close is the interdependence of these two species ! 

Similar relations can be traced in every group of ani- 
mals. When the salmon cease to run in the Sacramento 
Eiver in California the otter which feeds on them takes, it 
is said, to robbing the poultry-yards ; and the bear, which 
also feeds on fish, strikes out for other game, taking fruit 
or chickens or bee-hives, whatever he may find. 



CHAPTER XXI 

ADAPTATIONS 

253. Origin of adaptations. — The strife for place in the 
crowd of animals makes it necessary for each one to adjust 
itself to the place it holds. As the individual becomes 
fitted to its condition, so must the species as a whole. The 
species is therefore made up of individuals that are fitted 
or may become fitted for the conditions of life. As the 
stress of existence becomes more severe, the individuals fit 
to continue the species are chosen more closely. This 
choice is the automatic work of the conditions of life, but 
it is none the less, effective in its operations, and in the 
course of centuries it becomes unerring. When conditions 
change, the perfection of adaptation in a species may be 
the cause of its extinction. If the need of a special fitness 
can not be met immediately, the species will disappear. 
For example, the native sheep of England have developed 
a long wool fitted to protect them in a cool, damp climate. 
Such sheep transferred to Cuba died in a short time, leav- 
ing no descendants. The warm fleece, so useful in Eng- 
land, rendered them wholly unfit for survival in the tropics. 
It is one advantage of man, as compared with other forms 
of life, that so many of his adaptations are external to his 
structure, and can be cast aside when necessity arises. 

254. Classification of adaptations. — The various forms of 
adaptations may be roughly divided into five classes, as fol- 
lows : (a) food securing, (b) self-protection, (c)rivalry, (d) 
defense of young, (e) surroundings. 

The few examples which are given under each class, 
290 



ADAPTATIONS 291 

some of them striking, some not especially so, are mostly 
chosen from the vertebrates and from the insects, because 
these two groups of animals are the groups with which be- 
ginning students of zoology are likely to be familiar, and 
the adaptations referred to are therefore most likely to bf 
best appreciated. Quite as good and obvious examples could 
be selected from any other groups of animals. The student 



Fig. 156.— The deep-sea angler {Coivjnolophus reinhardti), which has a dorsal spine 
modified to be a luminous "fishing rod and lure." attracting lantern-fishes 
(Echiostoma and ^thoprora). An extraordinary adaptation for securing food. 
(The angler is drawn after a figure of Lutken's.) 

will find good practice in trying to discover examples shown 
by the animals with which he may be familiar. That all 
or any part of the body structure of any animal can be 
called with truth an example of adaptation is plain from 
what we know of how the various organs of the animal 
body have come to exist. But by giving special attention 
to such adaptations as are plainly obvious, beginning stu- 



292 



ANIMAL STUDIES 



dents may be put in the 
way of independent ob- 
servation along an ex- 
tremely interesting and 
attractive line of zoolog- 
ical study. 

255. Adaptations for 
securing food. — For the 
purpose of capture of 
their prey, some carniv- 
orous animals are pro- 
vided with strong claws, 
sharp teeth, hooked 
beaks, and other struc- 
tures familiar to us in 
the lion, tiger, dog, cat, 
owl, and eagle. Insect- 
eating mammals have 
contrivances especially 




sac, which it uses in catching aud holding 
fishes that form its food. 





Fig. 158.— Foot of the bald eagle, 
showing claws for seizing its prey. 
(Chapman.; 



adapted for the catching of insects. The 
ant-eater, for example, has a 
curious, long sticky tongue 
which it thrusts forth from 
its cylindrical snout deep 
into the recesses of the ant- 
hill, bringing it out with its 
sticky surface covered with 
ants. Animals which feed on 
nuts are fitted with strong 
teeth or beaks for crack- 
ing them. Similar teeth are 
found in those fishes which 
feed on crabs, snails, or sea-ur- 
chins. Those mammals like 
the horse and cow, that 
feed on plants, have usually 



ADAPTATIONS 



293 



broad chisel-like incisor teeth for cutting off the foliage, 
and teeth of very similar form are developed in the dif- 
ferent groups of plant- 
eating fishes. Molar 
teeth are found when it 





Fig. 159.— Scorpion, showing the special devel- 
opment of certain mouth parts (the maxil- 
lary palpi) as pincer-like organs for grasp- 
ing prey. At the posterior tip of the body 
is the poisonous sting. 



Fig. 160.— Head of mosquito (fe- 
male), showing the piercing 
needle-like mouth parts which 
compose the "bill." 



is necessary that the food should be crushed or chewed, 
and the sharp canine teeth go with a flesh diet. The 
long neck of the giraffe en- 
ables it to browse on the 
foliage of trees in grassless 
regions. 

Insects like the leaf- 
beetles and the grasshop- 
pers, that feed on the 
foliage of plants, have a _ «.„ _ . , ir .. . ... 

° I ' Fig. 161.— The praying-horse {Mantis) with 

pair of jaWS, broad but fore legs developed as grasping organs. 




294 



ANIMAL STUDIES 



sharply edged, for cutting oft. bits of leaves and stems. 
Those which take only liquid food, as the butterflies and 
sucking-bugs, have their mouth parts modified to form a 
slender, hollow sucking beak or proboscis, which can be 
thrust into a flower nectary, 
or into the green tissue of 
plants or the flesh of animals, 
to suck up nectar or plant sap 
or blood, depending on the 
special food habits of the in- 
sect. The honey-bee has a 
very complicated equipment 
of mouth parts fitted for tak- 
ing either solid food like pol- 
len, or liquid food like the 
nectar of flowers. The mos- 
quito has a "bill" (Fig. 160) 
composed of six sharp, slender 
needles for piercing and lac- 
erating the flesh, and a long 
tubular under lip through 
which the blood can flow into 
the mouth. Some predaceous 
insects, as the praying-horse 
(Fig. 161), have their fore 
legs developed into formidable 
grasping organs for seizing and 
holding their prey. 

256. Adaptation for self-de- 
fense. — For self-protection, car- 
nivorous animals use the same 
weapons to defend themselves 
which serve to secure their 
prey; but these as well as 
other animals may protect themselves in other fashions. 
Most of the hoofed animals are provided with horns, struc- 




Fig. 162.— Acorns put into bark of tree 
by the Californian woodpecker 
(Melanerpes formicivorus bairdii). 
—From photograph, Stanford Uni- 
versity, California. 



ADAPTATIONS 



295 




Fig. 163.— Section of bark of live oak tree with acorns placed in it by the Californian 
woodpecker {Melanerpes formicixorus bairdii).— From photograph, Stanford 
University, California. 



tures useless in procuring food but often of great effective- 
ness as weapons of defense. To the category of structures 
useful for self-defense belong the many peculiarities of col- 
oration known as "recognition marks/' These are marks, 



296 



ANIMAL STUDIES 



not otherwise useful, which are supposed to enable mem- 
bers of any one species to recognize their own kind among 
the mass of animal life. To this category belongs the 
black tip of the weasel's tail, which re- 
mains the same whatever the changes 
in the outer fur. Another example is 
seen in the white outer feathers of the 
tail of the meadow-lark as well as in 
certain sparrows and warblers. The 
white on the skunk's back and tail 
serves the same purpose and also as a 
warning. It is to the skunk's advan- 
tage not to be hidden, for to be seen in 
the crowd of animals is to be avoided 
by them. The songs of birds and the 
calls of vnrious creatures serve also as 
recognition marks. Each species knows 
and heeds its own characteristic song 
or cry, and it is a source of mutual 
protection. The fur-seal pup knows 
its mother's call, even though ten thou- 
sand other mothers are calling on the 
rookery. 

The ways in which animals make 
themselves disagreeable or dangerous 
to their captors are almost as varied as the animals them- 
selves. Besides the teeth, claws, and horns of ordinary 
attack and defense, we find among the mammals many 
special structures or contrivances which serve for de- 
fense through making their possession unpleasant. The 
scent glands of the skunk and its relatives are noticed 
above. The porcupine has the bristles in its fur specialized 
as quills, barbed and detachable. These quills fill the 
mouth of an attacking fox or wolf, and serve well the pur- 
pose of defense. The hedgehog of Europe, an animal of 
different nature, being related rather to the mole than to 




Fig. 164.— Centiped. The 
foremost pair of legs is 
modified to be a pair of 
seizing and stinging or- 
gans. An adaptation 
for self-defense and for 
securing food. 



ADAPTATIONS 



297 



the squirrel, has a similar armature of quills. The armadillo 
of the tropics has movable shields, and when it withdraws its 





Fig. 165.— Flying fishes. (The upper one a species of Cypselurus, the lower of Exocm- 
tus.) These fishes escape from their enemies by leaping into the air and sailing 
or "flying" long distances. 



head (which is also defended by ; 
protected as a turtle. 



bony shield) it is as well 




Fig. 166. — The horned xoa.(i{Phrynosoma blainviUei). 
enemies. 



The spiny covering repels many 



Special organs for defense of this nature are rare among 
birds, but numerous among reptiles. The turtles are all 
20 



298 



ANIMAL STUDIES 



protected by bony shields, and some of them, the box-tur- 
tles, may close their shields almost hermetically. The 
snakes broaden their heads, swell their necks, or show their 
forked tongues to frighten their enemies. Some of them 



Fig. 167.— Noki or poisonous scorpion-fish (Emmydrichthys vulcanite) with poison- 
ous spines, from Tahiti. 



are further armed with fangs connected with a venom gland, 
so that to most animals their bite is deadly. Besides its 
fangs the rattlesnake has a rattle on the tail made up of a 




Fig. 168.— Mad torn {Scliilbeodes furiosus) with poisoned pectoral spine. 

succession of bony clappers, modified vertebrae, and scales, 
by which intruders are warned of their presence. This 
sharp and insistent buzz is a warning to animals of other 
species and a recognition signal to those of its own kind. 



ADAPTATIONS 



299 




Even the fishes have many modes of self-defense through 
giving pain or injury to those who would swallow them. 
The cat-fishes or horned pouts when attacked set immov- 
ably the sharp spine of the 
pectoral fin, inflicting a 
jagged wound. Pelicans 
who have swallowed a cat- 
fish have been known to 
die of the wounds inflicted 
by the fish's spine. In 
the group of scorpion- 
fishes and toad-fishes are 
certain genera in which 
these spines are provided 
with poison glands. These 
may inflict very severe 
wounds to other fishes, or 
even to birds or man. One of this group 
of poison-fishes is the noki {Emmydrich- 
thys, Fig. 167). A group of small fresh- 
water cat-fishes, known as the mad toms 
(Fig. 168), have also a poison gland attached 
to the pectoral spine, and its sting is most 
exasperating, like the sting of a wasp. 
The sting-rays (Fig. 169) of many species 
have a strong, jagged spine on the tail, 
covered with slime, and armed with broad 
saw -like teeth. This inflicts a dangerous wound, not 
through the presence of specific venom, but from the dan- 
ger of blood poisoning arising from the slime, and the 
ragged or unclean cut. 

Many fishes are defended by a coat of mail or a coat of 
sharp thorns. The globe-fishes and porcupine-fishes (Fig. 
170) are for the most part defended by spines, but their 
instinct to swallow air gives them an additional safeguard. 
When one of these fishes is disturbed it rises to the surface, 




Fig. 169.— A sting-ray 
{Urolophus goodei), 
from Panama. 



300 



ANIMAL STUDIES 










gulps air until its capacious stomach is filled, and then 
floats belly upward on the surface. It is thus protected 
from other fishes, though easily taken by man. The torpe- 
do, electric eel, electric cat-fish, and star-gazer, surprise and 

stagger their captors by 
means of electric shocks. 
In the torpedo or electric 
ray (Fig. 171), found on 
the sandy shores of all 
warm seas, on either side 
of the head is a large 
honeycomb-like structure 
which yields a strong 
electric shock whenever 
the live fish is touched. 
This shock is felt severe- 
ly if the fish be stabbed 
with a knife or metallic 
spear. The electric eel 
of the rivers of Para- 
guay and southern Bra- 
zil is said to give severe 
shocks to herds of wild 
horses driven through 
the streams, and similar 
accounts are given of the 
electric cat-fish of the 
Kile. 

Among the insects, 
the possession of stings 
is not uncommon. The 
wasps and bees are fa- 
miliar examples of stinging insects, but many other kinds, 
less familiar, are similarly protected. All insects have 
their bodies covered with a coat of armor, composed of a 
horny substance called chitin. In some cases this chitin- 




Fig. 170.— Porcupine-fish (Diodon hystrix), the 
lower ones swimming normally, the upper 
one floating belly upward, with inflated 
stomach.— Drawn from specimens from the 
Florida Keys. 



ADAPTATIONS 



301 



ous coat is very thick and serves to protect them effectu- 
ally. This is especially true of the beetles. Some insects 
are inedible (as mentioned in Chapter XXIV), and are con- 
spicuously colored so as to be readily recognized by in- 
sectivorous birds. The birds, knowing by experience that 
these insects are ill-tasting, avoid them. Others are ef- 
fectively concealed from their enemies by their close 
resemblance in color and marking to their surroundings. 
These protective resem- 
blances are discussed in 
Chapter XXIV. 

257. Adaptation for rival- 
ry. — In questions of attack 
and defense, the need of meet- 
ing animals of their own kind 
as well as animals of other 
races must be considered. In 
struggles of species with 
those of their own kind, the 
term rivalry may be applied. 
Actual warfare is confined 
mainly to males in the breed- 
ing season and to polyga- 
mous animals. Among those 
in which the male mates 
with many females, he must 
struggle with other males for 
their possession. In all the 
groups of vertebrates the 
sexes are about equal in num- 
bers. Where mating exists, 
either for the season or for 
life, this condition does not involve serious struggle or 
destructive rivalry. 

Among monogamous birds, or those which pair, the 
male courts the female of his choice by song and by display 




;. 171. — Torpedo or electric ray (NaT- 
cine brasiliensis), showing electric 
cells. 



302 



ANIMAL STUDIES 



of his bright feathers. The female consents to be chosen 
by the one which pleases her. It is believed that the hand- 
somest, most vivacious, and most musical males are the 
ones most successful in such courtship. With polygamous 
animals there is intense rivalry among the males in the 
mating season, which in almost all species is in the spring. 
The strongest males survive and reproduce their strength. 
The most notable adaptation is seen in the superior 
size of teeth, horns, mane, or spurs. Among the polyga- 
mous fur seals and sea lions the male is about four times 




Fig. 172.— A wild duck {Aylhya) family. Male, female, and praecocial young. 

the size of the female. In the polygamous family of deer, 
buffalo, and the domestic cattle and sheep, the male is larger 
and more powerfully armed than the female. In the polyg- 
amous group to which the hen, turkey, and peacock belong 
the males possess the display of plumage, and the structures 
adapted for fighting, with the will to use them. 

258. Adaptations for the defense of the young. — The pro- 
tection of the young is the source of many adaptive struc- 
tures as well as of the instincts by which such structures are 



ADAPTATIONS 



303 



utilized. In general, those animals are highest in develop- 
ment, with best means of holding their own in the struggle 




Fig. 173.— The altricial nestlings of the Blue jay (Cyanocitta ci^istata). 

for life, that take best care of their young. The homes 
of animals are specially discussed in the volume on Ani- 



304 



ANIMAL STUDIES 



mal Life, but those instincts which lead to home-building 
may all be regarded as useful adaptations in preserving 
the young. Among the lower or more coarsely organized 



%am 








Kangaroo (Macropvs rufus) with young in pouch. 



ADAPTATIONS 



305 




birds, such as the chicken, the duck, and the auk, as with 
the reptiles, the young animal is hatched with well-devel- 
oped muscular system and sense 
organs, and is capable of running 
about, and, to some extent, of feed- 
ing itself. Birds of this type are 
known as prcecocial (Fig. 172), while 
the name altricial (Fig. 173) is ap- 
plied to the more highly organized 
forms, such as the thrushes, doves, 
and song-birds generally. With 
these the young are hatched in a 
wholly helpless condition, with in- 
effective muscles, deficient senses, 
and dependent wholly upon the 
parent. The altricial condition de- 
mands the building of a nest, the 
establishment of a home, and the 

Fig. 175. — Esrg-case of Calif ornia j_« n _e -u j.t_ £ 

barn-door "skate (RajaMnocu- continued care of one or both of 

lata) cut open to show young the parents. 

inside. (Young issues natu- mi -, -, -\ 

rally at one end of the case.) The Vei 7 l°west mammals known, 

the duck-bills (Monotremes) of 
Australia, lay large eggs in a strong shell like those of a 
turtle, and guard them with great jealousy. But with 
almost all mammals the egg is very small and without 
much food-yolk. The egg begins its development within 
the body. It is nourished by the 
blood of the mother, and after birth 
the young is cherished by her, and 
fed by milk secreted by specialized 
glands of the skin. All these features 
are adaptations tending toward the 
preservation of the young. In the 
division of mammals next lowest to the Monotremes- 
kangaroo, opossum, etc. — the young are born in a very im- 
mature state and are at once seized by the mother and 




-Egg-case of the cock- 
roach. 



-the 



306 



ANIMAL STUDIES 



thrust into a pouch or fold of skin along the abdomen, 
where they are kept until they are able to take care of them- 
selves (Fig. 174). This is an interesting and ingenious 
adaptation, but less specialized and 
less perfect an adaptation than the 
conditions found in ordinary mam- 
mals. 

Among the insects, the special 
provisions for the protection and 
care of the eggs and the young are 
wide-spread and various. Some of 
those adaptations which take the 
special form of nests or " homes " 
are described in the volume on 
Animal Life. The eggs of the 
common cockroach are laid in small 
packets inclosed in a firm wall (Fig. 
176). The eggs of the great water-bugs are carried on 
the back of the male (Fig. 177) ; and the spiders lay their 
eggs in a silken sac or cocoon, and some of the ground or 




Fig. 177. — Giant water -bug 
(Serphus). Male carrying 
eggs on its back. 



Fig. 178.— Cocoon inclosing the pupa of the great Ceanothus moth. Spun of silk by 
the larva before pupation. 

running spiders {Lycosiclce) drag this egg-sac, attached to 
the tip of the abdomen, about with them. The young 
spiders when hatched live for some days inside this sac. 
feeding on each other ! Many insects have long, sharp 



ADAPTATIONS 



307 



piercing ovipositors, by means of which the eggs are de- 
posited in the ground or in the leaves or stems of green 
plants, or even in the hard wood of tree-trunks. Some of 




-e s. 



the scale insects se- 
crete wax from their 
bodies and form a 
large, often beautiful 
egg-case, attached to 
and nearly covering the body in 
which eggs are deposited (Fig. 
179). The various gall insects 
lay their eggs in the soft tissue 
of plants, and on the hatching of 
the larvae an abnormal growth 
of the plant occurs about the 
young insect, forming an in- 
closing gall that serves not only 
to protect the insect within, 
but to furnish it with an abun- 
dance of plant-sap, its food. The 
young insect remains in the gall 
until it completes its develop- 
ment and growth, when it 
gnaws its way out. Such insect galls are especially abun- 
dant on oak trees (Fig. 180). The care of the eggs and the 
young of the social insects, as the bees and ants, are de- 
scribed in Chapter XXII. 




Fig. 179.— The cottony cushion scale 
insect {leery a purchasi), from 
California. The male is winged, 
the female wingless and with a 
large waxen egg-sac (e.s.) attached 
to her body. (The lines at the left 
of each figure indicate the size of 
the insects.) 



308 ANIMAL STUDIES 

259. Adaptations concerned with surroundings in life. — A 
large part of the life of the animal is a struggle with the 
environment itself; in this struggle only those that are 
adapted live and leave descendants fitted like themselves. 
The fur of mammals fits them to their surroundings. As 
the fur differs, so may the habits change. Some animals 
are active in winter ; others, as the bear, hibernate, sleep- 
ing in caves or hollow trees or in burrows until conditions 
are favorable for their activity. Most snakes and lizards 
hibernate in cold weather. In the swamps of Louisiana, 




% 



Fig. 180. —The giant gall of the white oak (California), made by the gall insect Andri- 
cus californicus. The gall at the right cut open to show tunnels made by the 
insects in escaping from the gall.— From photograph. 

in winter, the bottom may often be seen covered with water 
snakes lying as inert as dead twigs. Usually, however, 
hibernation is accompanied by concealment. Some animals 
in hibernation may be frozen alive without apparent injury. 
The blackfish of the Alaska swamps, fed to dogs when 
frozen solid, has been known to revive in the heat of the 
dog's stomach and to wriggle out and escape. As animals 
resist heat and cold by adaptations of structure or habits, 
so may they resist dryness. Certain fishes hold reservoirs 



ADAPTATIONS 



309 



of water above their gills, by means of which they can 
breathe during short excursions from . the water. Still 
others (mud-fishes) retain the primitive lung-like structure 
of the swim-bladder, and are able to breathe air when, in the 
dry season, the water of the pools is reduced to mud. 

Another series of adaptations is concerned with the 
places chosen by animals for their homes. The fishes that 
live in water have special organs for 
breathing under water (Fig. 182). 
Many of the South American mon- 
keys have the tip of the tail adapted 
for clinging to limbs of trees or to 
the bodies of other monkeys of its 
own kind. The hooked claws of the 
bat hold on to rocks, the bricks of 
chimneys, or to the surface of hollow 
trees where the bat sleeps through 
the day. The tree-frogs (Fig. 183) or 
tree-toads have the tips of the toes 
swollen, forming little pads by which 
they cling to the bark of trees. 

Among other adaptations relat- 
ing to special surroundings or con- 
ditions of life are the great cheek 
J pouches of the pocket gophers, 

which carry off the soil dug up by 
the large shovel-like feet when the 
gopher excavates its burrow. 
. „ , . Those insects which live under- 

Fig. 181.— Insect galls on leaf. 

ground, making burrows or tunnels 
in the soil, have their legs or other parts adapted for dig- 
ging and burrowing. The mole cricket (Fig. 184) has its 
legs stout and short, with broad, shovel-like feet. Some 
water-beetles (Fig. 185) and water-bugs have one or more of 
the pairs of legs flattened and broad to serve as oars or pad- 
dles for swimming. The grasshoppers or locusts, who leap. 




310 



ANIMAL STUDIES 



have their hind legs greatly enlarged and elon- 
gated, and provided with strong muscles, so as 
to make of them "leaping legs." The grubs 




Fig. 182.— Head of rainbow trout (Salmo irideus) with gill cover bent back to show 
gills, the breathing organs. 

or larvae of beetles which live as " borers " in tree-trunks 
have mere rudiments of legs, or none at all (Fig. 186). 
They have great, strong, biting jaws for cutting away 
the hard wood. They move simply by wriggling along 
in their burrows or tunnels. 

Insects that live 
in water either come 
up to the surface to -£ 
breathe or take down 
air underneath their " 
wings, or in some 
other way, or have 
gills for breathing the 
air which is mixed 
with the water. These 
gills are special adap- 
tive structures which present a great variety of form and 
appearance. In the young of the May-flies they are deli- 
cate plate-like flaps projecting from the sides of the body. 
They are kept in constant motion, gently waving back and 




Fig. 183.— Tree-toad {Hyla regilla). 



ADAPTATIONS 



311 



forth in the water so as to maintain currents to bring fresh 
water in contact with them. Young mosquitoes (Fig. 187) 

do not have gills, but come 
up to the surface to breathe. 
The larvae, or wrigglers, 
breathe through a special 





Fig. 184.— The mole cricket ( Gryllotalpa), 
with fore feet modified for digging. 



Fig. 185.— A water-beetle {Hydroph- 
ilus). 



tube at the posterior tip of the body, while the pupae have 
a pair of horn-like tubes on the back of the head end of 
the body. 

260. Degree of structural change in adaptations. — While 
among the higher or vertebrate animals, especially the 
fishes and reptiles, most remarkable cases of adaptations 
occur, yet the structural changes are for the most part ex- 
ternal, never seriously affecting the development of the 
internal organs other 
than the skeleton. The / \\\ \A/ 1 
organization of these J ^- m iWrry. y y/rfi . / m 
higher animals is much ®& 
less plastic than among , 
the invertebrates. In 

general, the higher the type the more persistent and un- 
changeable are those structures not immediately exposed 




312 



ANIMAL STUDIES 



to the influence of the struggle for existence. It is thus 
the outside of an animal that tells where its ancestors 
have lived. The inside, suffering little change, whatever 
the surroundings, tells the real nature of the animal. 

261. Vestigial organs. — In general, all the peculiarities of 
animal structure find their explanation in some need of 
adaptation. When this need ceases, the structure itself 
tends to disappear or else to serve some other need. In 
the bodies of most animals there are certain incomplete 
or rudimentary organs 
or structures which 
serve no distinct use- 
ful purpose. They are 
structures which, in the 
ancestors of the ani- 
mals now possessing 
them, were fully devel- 
oped functional organs, 
but which, because of a 
change in habits or con- 
ditions of living, are of 
no further need, and 
are gradually dying out. 
Such organs are called 
vestigial organs. Ex- 
amples are the disused 
ear muscles of man, the 
vermiform appendix in 
man, which is the reduced and now useless anterior end 
of the large intestine. In the lower animals, the thumb or 
degenerate first finger of the bird with its two or three little 
quills serves as an example. So also the reduced and elevated 
hind toe of certain birds, the splint bones or rudimentary 
side toes of the horse, the rudimentary eyes of blind fishes, 
the minute barbel or beard of the horned dace or chub, and 
the rudimentary teeth of the right whales and sword-fish. 




Fig. 187.— Young stages of the mosquito, 
a, larva (wriggler) ; b, pupa. 



ADAPTATIONS 



313 



Each of these vestigial organs tells a story of some past 
adaptation to conditions, one that is no longer needed in 
the life of the species. They have the same place in the 
study of animals that silent letters have in the study of 
words. For example, in our word knight the Tc and gh are 
no longer sounded ; but our ancestors used them both, as 
the Germans do to-day in their cognate word Knecht. So 
with the French word temps, which means time, in which 
both -p and s are silent. The Eomans, from whom the 
French took this word, needed all its letters, for they spelled 
and pronounced it tempus. In general, every silent letter 
in every word was once sounded. In like manner, every 
vestigial structure was once in use and helpful or necessary 
to the life of the animal which possessed it. 




Horns of two male elk interlocked while fighting. 
; Permission of G. O. Shields, publisher of Recreation.) 



CHAPTEE XX11 

ANIMAL. COMMUNITIES AND SOCIAL LIFE 

262. Man not the only social animal — Man is commonly 
called the social animal, but he is not the only one to 
which this term may be applied. There are many others 
which possess a social or communal life. A moment's 
thought brings to mind the familiar facts of the communal 
life of the honey-bee and of the ants. And there are many 
other kinds of animals, not so well known to us, that live 
in communities or colonies, and live a life which in greater 
or less degree is communal or social. In this connection 
we may use the term communal for the life of those ani- 
mals in which the division of labor is such that the indi- 
vidual is dependent for its continual existence on the com- 
munity as a whole. The term social life would refer to a 
lower degree of mutual aid and mutual dependence. 

263. The honey-bee. — Honey-bees live together, as we 
know, in large communities. We are accustomed to think 
of honey-bees as the inhabitants of bee-hives, but there 
were bees before there were hives. The "bee-tree" is 
familiar to many of us. The bees, in Xature, make their 
home in the hollow of some dead or decaying tree-trunk, 
and carry on there all the industries which characterize 
the busy communities in the hives. A honey-bee com- 
munity comprises three kinds of individuals (Fig. 188) — 
namely, a fertile female or queen, numerous males or 
drones, and many infertile females or workers. These 
three kinds of individuals differ in external appearance 
sufficiently to be readily recognizable. The workers are 

3U 



ANIMAL COMMUNITIES AND SOCIAL LIFE 315 

smaller than the queens and drones, and the last two differ 
in the shape of the abdomen, or hind body, the abdomen of 
the queen being longer and more slender than that of the 




Fig. 188.— Honey-bee. a, drone or male ; b, worker or infertile female ; c, queen or 
fertile female. 

male or drone. In a single community there is one queen, 
a few hundred drones, and ten to thirty thousand workers. 
The number of drones and workers varies at different 
times of the year, being smallest in winter. Each kind of 
individual has certain work or business to do for the whole 
community. The queen lays all the eggs from which new 
bees are born; that is, she is the mother of the entire 
community. The drones or males have simply to act as 
royal consorts ; upon them depends the fertilization of the 
eggs. The workers undertake all the food-getting, the 
care of the young bees, the comb-building, the honey-mak- 
ing — all the industries with which we are more or less 
familiar that are carried on in the hive. And all the 
work done by the workers is strictly work for the whole 
community ; in no case does the worker bee work for itself 
alone ; it works for itself only in so far as it is a member 
of the community. 

How varied and elaborately perfected these industries 
are may be perceived from a brief account of the life his- 
tory of a bee community. The interior of the hollow in 
the bee-tree or of the hive is filled with " comb " — that is, 
with wax molded into hexagonal cells and supports for 
these cells. The molding of these thousands of symmet- 



316 



ANIMAL STUDIES 



rical cells is accomplished by the workers by means of their 
specially modified trowel-like mandibles or jaws. The wax 
itself, of which the cells are made, comes from the bodies 
of the workers in the form of small 
liquid drops which exude from the skin 
on the under side of the abdomen or 
hinder body rings. These droplets 
run together, harden and become flat- 
tened, and are removed from the wax 
plates, as the peculiarly modified parts 
of the skin which produce the wax 
are called, by means of the hind legs, 
which are furnished with scissor-like 
contrivances for cutting off the wax 
(Fig. 189). In certain of the cells are 
stored the pollen and honey, which 
serve as food for the community. The 
pollen is gathered by the workers from 
certain favorite flowers and is carried 
by them from the flowers to the hive 
in the "pollen baskets," the slightly 
concave outer surfaces of one of the 
segments of the broadened and flattened 
hind legs. This concave surface is lined 
on each margin with a row of incurved 
stiff hairs which hold the pollen mass se- 
curely in place (Fig. 189). The " honey " 
is the nectar of flowers which has been 
sucked up by the workers by means of 
their elaborate lapping and sucking 
mouth parts and swallowed into a sort 
of honey-sac or stomach, then brought 
to the hive and regurgitated into the 
cells. This nectar is at first too watery to be good 
honey, so the bees have to evaporate some of this water. 
Many of the workers gather above the cells containing 




Fig. 189.— Poster 
worker honey-bee. The 
concave surface of the 
upper large joint with 
the marginal hairs is 
the pollen basket ; the 
wax shears are the cut- 
ting surfaces of the 
angle between the two 
large segments of the 
leg. 



ANIMAL COMMUNITIES AND SOCIAL LIFE 317 

nectar, and buzz — that is, vibrate their wings violently. 
This creates currents of air which pass over the exposed 
nectar and increase the evaporation of the water. The 
violent buzzing raises the temperature of the bees' bodies, 
and this warmth given off to the air also helps make evap- 
oration more rapid. In addition to bringing in food the 
workers also bring in, when necessary, " propolis," or the 
resinous gum of certain trees, which they use in repairing 
the hive, as closing up cracks and crevices in it. 

In many of the cells there will be found, not pollen or 
honey, but the eggs or the young bees in larval or pupal 

condition (Fig. 190). 
The queen moves 
about through the 
hive, laying eggs. 
She deposits only one 
egg in a cell. In 
three days the egg 
hatches, and the 
young bee • appears 
as a helpless, soft, 
white, footless grub 

Fig. 190.— Cells containing eggs, larvae, and pupa? of or larva. It is Cared 
the honey-bee. The lower large, irregular cells f Qr , certain f the 

are queen cells. — After Benton. j 

workers, that may be 
called nurses. These nurses do not differ structurally from 
the other workers, but they have the special duty of caring 
for the helpless young bees. They do not go out for pollen 
or honey, but stay in the hive. They are usually the new 
bees — i. e., the youngest or most recently added workers. 
After they act as nurses for a week or so they take their 
places with the food-gathering workers, and other new 
bees act as nurses. The nurses feed the young or larval 
bees at first with a highly nutritious food called bee-jelly, 
which the nurses make in their stomach, and regurgitate 
for the larvae. After the larvae are two or three days old 




318 ANIMAL STUDIES 

they are fed with pollen and honey. Finally, a small mass 
of food is put into the cell, and the cell is " capped " or 
covered with wax. The larva, after eating all the food, in 
two or three days more changes into a pupa, which lies 
quiescent without eating for thirteen days, when it changes 
into a full-grown bee. The new bee breaks open the cap 
of the cell with its jaws, and comes out into the hive, ready 
to take up its share of the work for the community. In a 
few cases, however, the life history is different. The nurses 
will tear down several cells around some single one, and 
enlarge this inner one into a great irregular vase-shaped 
cell. When the egg hatches, the grub or larva is fed bee- 
jelly as long as it remains a larva, never being given ordi- 
nary pollen and honey at all. This larva finally pupates, 
and there issues from the pupa not a worker or drone bee, 
but a new queen. The egg from which the queen is pro- 
duced is the same as the other eggs, but the worker nurses 
by feeding the larva only the highly nutritious bee-jelly 
make it certain that the new bee shall become a queen 
instead of a worker. It is also to be noted that the male 
bees or drones are hatched from eggs that are not ferti- 
lized, the queen having it in her power to lay either ferti- 
lized or unfertilized eggs. From the fertilized eggs hatch 
larvae which develop into queens or workers, depending on 
the manner of their nourishment ; from the unfertilized 
eggs hatch the males. 

When several queens appear there is much excitement 
in the community. Each community has normally a single 
one, so that when additional queens appear some rearrange- 
ment is necessary. This rearrangement comes about first 
by fighting among the queens until only one of the new 
queens is left alive. Then the old or mother queen issues 
from the hive or tree followed by many of the workers. 
She and her followers fly away together, finally alighting 
on some tree branch and massing there in a dense swarm. 
This is the familiar phenomenon of " swarming." The 



ANIMAL COMMUNITIES AND SOCIAL LIFE 319 

swarm finally finds a new hollow tree, or in the case of the 
hive-bee (Fig. 191) the swarm is put into a new hive, where 
the bees build cells, gather food, produce young, and thus 





Fig. 191.— Hiving a swarm of honey-bees. Photograph by S. J. Hunter. 

found a new community. This swarming is simply an emi- 
gration, which results in the wider distribution and in the 
increase of the number of the species. It is a peculiar but 
effective mode of distributing and perpetuating the species. 
There are many other interesting and suggestive things 
which might be told of the life in a bee community : how 
the community protects itself from the dangers of starva- 
tion when food is scarce or winter comes on by killing the 
useless drones and the immature bees in egg and larval 
stage ; how the instinct of home-finding has been so highly 
developed that the worker bees go miles away for honey 
and nectar, flying with unerring accuracy back to the hive ; 
of the extraordinarily nice structural modifications which 
adapt the bee so perfectly for its complex and varied busi- 
nesses ; and of the tireless persistence of the workers until 



320 



ANIMAL STUDIES 



they fall exhausted and dying in the performance of their 
duties. The community, it is important to note, is a per- 
sistent or continuous one. The workers do not live long, 
the spring broods usually not over two or three months, 
and the fall broods not more than six or eight months; 
but new ones are hatching while the old ones are dying, 
and the community as a whole always persists. The queen 
may live several years, perhaps as many as five.* She lays 
about one million eggs a year. 

264. The ants. — There are many species of ants, two 
thousand or more, and all of them live in communities and 
show a truly communal life. There is much variety of 
habit in the lives of different kinds of ants, and the degree 
in which the communal or social life is specialized or elab- 
orated varies much. But certain general conditions pre- 
vail in the life of all the different kinds of individuals — 




Fig. 192.— Female (a), male (6), and worker (c) of an ant {Camponotus ep.). 

sexually developed males and females that possess wings, 
and sexually undeveloped workers that are wingless (Fig. 
192). In some kinds the workers show structural differ- 

* A queen bee has been kept alive for fifteen years. 



ANIMAL COMMUNITIES AND SOCIAL LIFE 321 

ences among themselves, being divided into small workers, 
large workers, and soldiers. The workers are not, as with 
the bees, all infertile females, but they are both male and 
female, both being infertile. Although the life of the ant 
communities is much less familiar and fully known than 
that of the bees, it is even more remarkable in its speciali- 
zations and elaborateness. The ant home, or nest, or formi- 
cary, is, with most species, a very elaborate underground, 
many-storied labyrinth of galleries and chambers. Certain 
rooms are used for the storage of food ; certain others as 
" nurseries " for the reception and care of the young ; and 
others as stables for the ants' cattle, certain plant-lice or 
scale-insects which are sometimes collected and cared for by 
the ants. The food of ants comprises many kinds of vege- 
table and animal substances, but the favorite food, or " na- 
tional dish," as it has been called, is a sweet fluid which is 
produced by certain small insects, the plant-lice (Aphidae) 
and scale-insects (Coccidas). These insects live on the sap 
of plants ; rose-bushes are especially favored with their pres- 
ence. The worker ants (and we rarely see any ants but 
the wingless workers, the winged males and females appear- 
ing out of the nest only at mating time) find these honey- 
secreting insects, and gently touch or stroke them with their 
feelers (antennas), when the plant-lice allow tiny drops of 
the honey to issue from the body, which are eagerly drunk 
by the ants. It is manifestly to the advantage of the ants 
that the plant-lice should thrive ; but they are soft-bodied, 
defenseless insects, and readily fall a prey to the wander- 
ing predaceous insects like the lady-birds and aphis lions. 
So the ants often guard small groups of plant-lice, attack- 
ing, and driving away the would-be ravagers. When the 
branch on which the plant-lice are gets withered and dry, 
the ants have been observed to carry the plant-lice care- 
fully to a fresh, green branch. In the Mississippi Valley a 
certain kind of plant-louse lives on the roots of corn. Its 
eggs are deposited in the ground in the autumn and hatch 



322 ANIMAL STUDIES 

the following spring before the corn is planted. Xow, the 
common little brown ant lives abundantly in the corn- 
fields, and is specially fond of the honey secreted by the 
corn-root plant-louse. So, when the plant-lice hatch in the 
spring before there are corn roots for them to feed on, the 
little brown ants with great solicitude carefully place the 
plant-lice on the roots of a certain kind of knotweed which 
grows in the field, and protect them until the corn ger- 
minates. Then the ants remove the plant-lice to the roots 
of the corn, their favorite food plant. In the arid lands of 
Xew Mexico and Arizona the ants rear their scale-insects 
on the roots of cactus. Other kinds of ants carry plant- 
lice into their nests and provide them with food there. 
Because the ants obtain food from the plant-lice and take 
care of them, the plant-lice are not inaptly called the ants' 
cattle. 

Like the honey-bees, the young ants are helpless little 
grubs or larvae, and are cared for and fed by nurses. The 
so-called ants' eggs, little white, oval masses, which we 
often see being carried in the mouths of ants in and out of 
an ants' nest, are not eggs, but are the pupae which are 
being brought out to enjoy the warmth and light of the 
sun or being taken back into the nest afterward. 

In addition to the workers that build the nest and col- 
lect food and care for the plant-lice, there is in many 
species of ants a kind of individuals called soldiers. These 
are wingless, like the workers, and are also, like the work- 
ers, not capable of laying or of fertilizing eggs. It is the 
business of the soldiers, as their name suggests, to fight. 
They protect the community by attacking and driving 
away predaceous insects, especially other ants. The ants 
are among the most warlike of insects. The soldiers of a 
community of one species of ant often sally forth and 
attack a community of some other species. If successful 
in battle the workers of the victorious community take 
possession of the food stores of the conquered and carry 



ANIMAL COMMUNITIES AND SOCIAL LIFE 323 

them to their own nest. Indeed, they go even further ; they 
may make slaves of the conquered ants. There are numer- 
ous species of the so-called slave-making ants. The slave- 
makers carry into their own nest the eggs and larvae and 
pupae of the conquered community, and when these come 
to maturity they act as slaves of the victors — that is, they 
collect food, build additions to the nests, and care for the 
young of the slave-makers. This specialization goes so far 
in the case of some kinds of ants, like the robber-ant of 
South America (Uciton), that all of the Eciton workers have 
become soldiers, which no longer do any work for them- 
selves. The whole community lives, therefore, wholly by 
pillage or by making slaves of other kinds of ants. There 
are four kinds of individuals in a robber-ant community — 
winged males, winged females, and small and large wing- 
less soldiers. There are many more of the small soldiers 
than of the large, and some naturalists believe that the few 
latter, which are distinguished by heads and jaws of great 
size, act as officers. On the march the small soldiers are 
arranged in a long, narrow column, while the large soldiers 
are scattered along on either side of the column and appear 
to act as sentinels and directors of the army. The obser- 
vations made by the famous Swiss students of ants, Huber 
and Forel, and by other naturalists, read like fairy tales, 
and yet are the well-attested and often reobserved actual 
phenomena of the extremely specialized communal and 
social life of these animals. 

265. Other communal insects. — The termites or white 
ants (not true ants) are communal insects. Some species 
of termites in Africa live in great mounds of earth, often 
fifteen feet high. The community comprises hundreds of 
thousands of individuals, which are of eight kinds (Fig. 193), 
viz., sexually active winged males, sexually active winged 
females, other fertile males and females which are wingless, 
wingless workers of both sexes not capable of reproduc- 
tion, and wingless soldiers of both sexes also incapable of 



324 



ANIMAL STUDIES 



reproduction. The production of new individuals is the 
sole business of the fertile males and females ; the workers 
build the nest and collect food, and the soldiers protect the 
community from the attacks of marauding insects. The 
egg-laying queen grows to monstrous size, being sometimes 




Fig. 193.— Termites, a, queen ; ft, male ; c, worker ; d, soldier. 

five or six inches long, while the other individuals of the 
community are not more than half or three quarters of 
an inch long. The great size of the queen is due to the 
enormous number of eggs in her body. 

The bumble-bees live in communities, but their social 
arrangements are very simple ones compared with those of 
the honey-bee. There is, in fact, among the bees a series 
of gradations from solitary to communal life. The inter- 
esting little green carpenter-bees live a truly solitary life. 
Each female bores out the pith from five or six inches of 
an elder branch or raspberry cane, and divides this space 
into a few cells by means of transverse partitions (Fig. 194). 
In each cell she lays an egg, and puts with it enough food 
— flower pollen — to last the grub or larva through its life. 



ANIMAL COMMUNITIES AND SOCIAL LIFE 



325 



She then waits in an upper cell of the nest until the young 
bees issue from their cells, when she leads them off, and 
each begins active life on its own account. The mining- 




Fig. 194.— Nest of carpenter-bee. 



Fig. 195.— Nest of Andrena, the mining-bee. 



bees (Andrena), which make little burrows (Fig. 195) in a 
clay bank, live in large colonies — that is, they make their 
nest burrows close together in the same clay bank, but each 
female makes her own burrow, lays her own eggs in it, fur- 
nishes it with food — a kind of paste of nectar and pollen — 
and takes no further care of her young. Xor has she at 
any time any special interest in her neighbors. But with 
the smaller mining-bees, belonging to the genus Halictus, 
several females unite in making a common burrow, after 
which each female makes side passages of her own, extend- 



326 



ANIMAL STUDIES 



ing from the main or public entrance burrow. As a well- 
known entomologist has said, Andrena builds villages com- 
posed of individual homes, while Halictus makes cities 
composed of apartment houses. The bumble-bee (Fig. 196), 
however, establishes a real community with a truly com- 
munal life, although a very simple one. The few bumble- 
bees which we see in winter time are queens ; all other 
bumble-bees die in the autumn. In the spring a queen 
selects some deserted nest of a field-mouse, or a hole in 
the ground, gathers pollen which she molds into a rather 
large irregular mass and puts into 
the hole, and lays a few eggs on the 
pollen mass. The young grubs or 
larvae which soon hatch feed on the 
pollen, grow, pupate, and issue as 
workers — winged bees a little small- 
er than the queen. These workers 
bring more pollen, enlarge the nest, 
and make irregular cells in the pol- 
len mass, in each of which the queen 
lays an egg. She gathers no more 
pollen, does no more work except 
that of egg-laying. From these new 
eggs are produced more workers, and 
so on until the community may come 
to be pretty large. Later in the sum- 
mer males and females are produced 
and mate. With the approach of 
winter all the workers and males die, 
leaving only the fertilized females, 
the queens, to live through the win- 
ter and found new communities in 
the spring. 

The social wasps show a communal life like that of the 
bumble-bees. The only yellow-jackets and hornets that 
live through the winter are fertilized females or queens. 




Fig. 196.— Bumble-bees, a, 
worker ; b, queen or fer- 
tile female. 



ANIMAL COMMUNITIES AND SOCIAL LIFE 



327 



When spring comes each queen builds a small nest sus- 
pended from a tree branch, and consisting of a small comb 
inclosed in a covering or envelope open at the lower end. 
The nest is composed of " wasp paper," made by chewing 
bits of weather-beaten wood taken from old fences or out- 
buildings. In each of the cells the queen lays an egg. 
She deposits in the cell a small mass of food, consisting of 
some chewed insects or spiders. From these eggs hatch 
grubs which eat the food prepared for them, grow, pupate, 
and issue as worker bees, winged and slightly smaller 
than the queen (Fig. 197). The workers enlarge the nest, 
adding more combs and making many cells, in each of 
which the queen lays an egg. The workers provision the 
cell with chewed insects, and other broods of workers are 

rapidly hatched. The 
community grows in 
numbers and the nest 
grows in size until it 
comes to be the great 
ball-like oval mass which 
we know so well as a 
hornets' nest (Figs. 198 
and 199), a thing to be 
left untouched. Some- 
times the nest is built 
underground. When 
disturbed, they swarm 
out of the hole and 
fiercely attack any in- 
vading foe in sight. 
After a number of 
broods of workers has 
been produced, broods of males and females appear and 
mating takes place. In the late fall the males and all of 
the many workers die, leaving only the new queens to live 
through the winter. 




€ 



Fig. 197.— The yellow-jacket (Vespa), a social 
wasp, a, worker ; b, queen. 



328 



ANIMAL STUDIES 



The bumble-bees and social wasps show an intermediate 
condition between the simply gregarious or neighborly 




Fig. 198.— Nest of Vespa, a social 
wasp. From photograph. 



-Nest of Vespa opened to show 
combs within. 



mining-bees and the highly developed, permanent honey- 
bee community. Naturalists believe that the highly or- 
ganized communal life of the honey-bees and the ants is 
a development from some simple condition like that of the 
bumble-bees and social wasps, which in its turn has grown 
out of a still simpler, mere gregarious assembly of the 
individuals of one species. It is not difficult to see how 
such a development could in the course of a long time take 
place. 

266. Gregariousness and mutual aid. — The simplest form 
of social life is shown among those kinds of animals in 
which many individuals of one species keep together, form- 
ing a great band or herd. In this case there is not much 
division of labor, and the safety of the individual is not 
wholly bound up in the fate of the herd. Such animals are 



ANIMAL COMMUNITIES AND SOCIAL LIFE 329 

said to be gregarious in habit. The habit undoubtedly is 
advantageous in the mutual protection and aid afforded 
the individuals of the band. This mutual help in the case 
of many gregarious animals is of a very positive and obvious 
character. In other cases this gregariousness is reduced to 
a matter of slight or temporary convenience, possessing but 
little of the element of mutual aid. The great herds of 
reindeer in the north, and of the bison or buffalo which 
once ranged over the Western American plains, are examples 
of a gregariousness in which mutual protection from ene- 
mies, like wolves, seems to be the principal advantage gained. 
The bands of wolves which hunted the buffalo show the 
advantage of mutual help in aggression as well as in pro- 
tection. In this banding together of wolves there is active 
co-operation among individuals to obtain a common food 
supply. What one wolf can not do — that is, tear down a 
buffalo from the edge of the herd — a dozen can do, and all 
are gainers by the operation. On the other hand, the vast 
assembling of sea-birds (Fig. 200) on certain ocean islands 
and rocks is a condition probably brought about rather by 
the special suitableness of a few places for safe breeding 
than from any special mutual aid afforded ; still, these sea- 
birds undoubtedly combine to drive off attacking eagles 
and hawks. Eagles are usually considered to be strictly 
solitary in habit (the unit of solitariness being a pair, not 
an individual) ; but the description, by a Eussian naturalist, 
of the hunting habits of the great white-tailed eagle (Hali- 
cetos albicilla) on the Eussian steppes shows that this kind 
of eagle at least has adopted a gregarious habit, in which 
mutual help is plainly obvious. This naturalist once saw an 
eagle high in the air, circling slowly and widely in perfect 
silence. Suddenly the eagle screamed loudly. "Its cry 
was soon answered by another eagle, which approached it, 
and was followed by a third, a fourth, and so on, till nine 
or ten eagles came together and soon disappeared." The 
naturalist, following them, soon discovered them gathered 
22 



ANIMAL COMMUNITIES AND SOCIAL LIFE 331 

about the dead body of a horse. The food found by the 
first was being shared by all. The association of pelicans in 
fishing is a good example of the advantage of a gregarious 
and mutually helpful habit. The pelicans sometimes go 
fishing in great bands, and, after having chosen an appro- 
priate place near the shore, they form a wide half-circle 
facing the shore, and narrow it by paddling toward the 
land, catching the fish which they inclose in the ever-nar- 
rowing circle. 

The wary Eocky Mountain sheep live together in small 
bands, posting sentinels whenever they are feeding or rest- 
ing, who watch for and give warning of the approach of 
enemies. The beavers furnish a well-known and very inter- 
esting example of mutual help, and they exhibit a truly 
communal life, although a simple one. They live in " vil- 
lages " or communities, all helping to build the dam across 
the stream, which is necessary to form the broad marsh 
or pool in which the nests or houses are built. Prairie- 
dogs live in great villages or communities which spread 
over many acres. They tell each other by shrill cries 
of the approach of enemies, and they seem to visit each 
other and to enjoy each other's society a great deal, 
although that they afford each other much actual active 
help is not apparent. Birds in migration are gregarious, 
although at other times they may live comparatively alone. 
In their long flights they keep together, often with definite 
leaders who seem to discover and decide on the course 
of flight for the whole great flock. The wedge-shaped 
flocks of wild geese flying high and uttering their sharp, 
metallic call in their southward migrations are well known 
in many parts of the United States. Indeed, the more 
one studies the habits of animals the more examples of 
social life and mutual help will be found. Probably most 
animals are in some degree gregarious in habit, and in all 
cases of gregariousness there is probably some degree of 
mutual aid. 



332 ANIMAL STUDIES 

267. Division of labor and communal life. — It has been 
explained in Animal Life that the complexity of the 
bodies of the higher animals depends on a specialization or 
differentiation of parts, due to the assumption of different 
functions or duties by different parts of the body ; that the 
degree of structural differentiation depends on the degree 
or extent of division of labor shown in the economy of the 
animal. It is obvious that the same principle of division of 
labor with accompanying modification of structure is the 
basis of colonial and communal life. It is simply a mani- 
festation of the principle among individuals instead of 
among organs. The division of the necessary labors of life 
among the different zooids of the colonial jelly-fish is plain- 
ly the reason for the profound and striking, but always 
reasonable and explicable modifications of the typical polyp 
or medusa body, which is shown by the swimming zooids, 
the feeding zooids, the sense zooids, and the others of the 
colony. And similarly in the case of the termite commu- 
nity, the soldier individuals are different structurally from 
the worker individuals because of the different work they 
have to do. And the queen differs from all the others, be- 
cause of the extraordinary prolificacy demanded of her to 
maintain the great community. 

It is important to note, however, that among those ani- 
mals that show the most highly organized or specialized 
communal or social life, the structural differences among 
the individuals are the least marked, or at least are not the 
most profound. The three kinds of honey-bee individuals 
differ but little; indeed, as two of the kinds, male and 
female, are to be found in the case of almost all kinds of 
animals, whether communal in habit or not, the only unu- 
sual structural specialization in the case of the honey-bee, is 
the presence of the worker individual, which differs from 
the usual individuals in but little more than the rudimen- 
tary condition of the reproductive glands. Finally, in the 
case of man, with whom the communal or social habit is so 



ANIMAL COMMUNITIES AND SOCIAL LIFE 333 

all-important as to gain for him the name of " the social 
animal," there is no differentiation of individuals adapted 
only for certain kinds of work. Among these highest 
examples of social animals, the presence of an advanced 
mental endowment, the specialization of the mental power, 
the power of reason, have taken the place of and made 
unnecessary the structural differentiation of individuals. 
The honey-bee workers do different kinds of work : some 
gather food, some care for the young, and some make wax 
and build cells, but the individuals are interchangeable; 
each one knows enough to do these various things. There 
is a structural differentiation in the matter of only one 
special work or function, that of reproduction. 

With the ants there is, in some cases, a considerable 
structural divergence among individuals, as in the genus 
Atta of South America with six kinds of individuals — 
namely, winged males, winged females, wingless soldiers, 
and wingless workers of three distinct sizes. In the case 
of other kinds with quite as highly organized a communal 
life there are but three kinds of individuals, the winged 
males and females and the wingless workers. The workers 
gather food, build the nest, guard the " cattle " (aphids), 
make war, and care for the young. Each one knows enough 
to do all these various distinct things. Its body is not so 
modified that it can do but one kind of thing, which thing 
it must always do. 

The increase of intelligence, the development of the 
power of reasoning, is the most potent factor in the devel- 
opment of a highly specialized social life. Man is the 
example of the highest development of this sort in the ani- 
mal kingdom, but the highest form of social development 
is not by any means the most perfectly communal. 

268. Advantages of communal life. — The advantages of 
communal or social life, of co-operation and mutual aid, are 
real. The animals that have adopted such a life are among 
the most successful of all animals in the struggle for exist- 



334 ANIMAL STUDIES 

ence. The termite individual is one of the most defense- 
less, and, for those animals that prey on insects, one of 
the most toothsome luxuries to be found in the insect 
world. But the termite is one of the most abundant and 
widespread and successfully living insect kinds in all the 
tropics. Where ants are not, few insects are. The honey- 
bee is a popular type of a successful life. The artificial 
protection afforded the honey-bee by man may aid in its 
struggle for existence, but it gains this protection because 
of certain features of its communal life, and in Xature the 
honey-bee takes care of itself well. The Little Bee People 
of Kipling's Jungle Book, who live in great communities in 
the rocks of Indian hills, can put to rout the largest and 
fiercest of the jungle animals. Co-operation and mutual 
aid are among the most important factors which help in 
the struggle for existence. Its great advantages are, how- 
ever, in some degree balanced by the fact that mutual help 
brings mutual dependence. The community or society can 
accomplish greater things than the solitary individuals, but 
co-operation limits freedom, and often sacrifices the indi- 
vidual to the whole. 



CHAPTEE XXIII 

COMMENSALISM AND PARASITISM 

269. Association between animals of different species. — 

The living together and mutual help discussed in the last 
chapter concerned in each instance a single species of ani- 
mal. All the various members of a pack of wolves or of a 
community of ants are individuals of the same species. 
But there are many instances of an association of individ- 
uals of different kinds of animals. In many cases of an 
association of individuals of different species one kind 
derives great benefit and the other suffers more or less 
injury from the association. One kind lives at the expense 
of the other. This association is called parasitism. In 
some cases, however, neither kind of animal suffers from 
the presence of the other. The two live together in har- 
mony and presumably to their mutual advantage. In some 
cases this mutual advantage is obvious. This kind of asso- 
ciation is called commensalism or symbiosis. 

270. Commensalism. — A curious example of commensal- 
ism is afforded by the different species of Eemoras (Echenei- 
clidcB) which attach themselves to sharks, barracudas, and 
other large fishes by means of a sucking disk on the top of 
the head (Fig. 201). This disk is made by a modification 
of the dorsal fin. The Eemora thus attached to a shark 
may be carried about for weeks, leaving its host only tG 
secure food. This is done by a sudden dash through the 
water. The Eemora injures the shark in no way save, per- 
haps, by the slight check its presence gives to the shark's 
speed in swimming. 

335 



336 ANIMAL STUDIES 

Whales, similarly, often carry barnacles about with 
them. These barnacles are permanently attached to the 
skin of the whale just as they would be to a stone or 



Fig. 201.— Remora, with dorsal fin modified to be a sucking plate by which the fish 
attaches itself to a shark. 

wooden pile. Many small crustaceans, annelids, mollusks, 
and other invertebrates burrow into the substance of living 
sponges for shelter. On the other hand, the little boring 
sponge (Oliofia) burrows in the shells of oysters and other 
bivalves for protection. Some species of sponge " are never 
found growing except on the backs or legs of certain 
crabs." In these cases the sponge, with its many plant-like 
branches, protects the crab by concealing it from its ene- 
mies, while the sponge is benefited by being carried about 
by the crab to new food supplies. 

Small fish of the genus Xomeus may often be found 
accompanying the beautiful Portuguese man-of-war {Plnj- 
salia) as it sails slowly about on the ocean's surface (Fig. 
202). These little fish lurk underneath the float and among 
the various hanging thread-like parts of the Plnjsalia, 
which are provided with stinging cells. 

In the nests of the various species of ants and termites 
many different kinds of other insects have been found. 
Some of these are harmful to their hosts, in that they feed 
on the food stores gathered by the industrious and provi- 
dent ant, but others appear to feed only on refuse or use- 
less substances in the nest. Some may even be of help to 
their hosts. Over one thousand species have been recorded 
by collectors as living habitually in the nests of ants and 
termites. 



COMMENSALISM AND PARASITISM 



337 



r 



271. Symbiosis. — Of a more intimate character, and of 
more obvious and certain mutual advantage, is the well- 
known association called symbiosis. The hermit-crab always 
takes for his habitation the shell of another animal, often 
that of the common whelk. 
All of the hind part of the 
crab lies inside the shell, while 
its head with its great claws 
project from the opening of 
the shell. On the surface of 
the shell near the opening 
there is often to be found a 
sea-anemone, or sea-rose (Fig. 
203). This sea-anemone is 
fastened securely to the shell, 
and has its mouth opening 
and tentacles near the head 
of the crab. The sea-anemone 
is carried from place to place 
by the hermit-crab, and in this 
way is much aided in obtain- 
ing food. On the other hand, 
the crab is protected from its 
enemies by the well-armed 
and dangerous tentacles of 
the sea-anemone. If the sea- 
anemone be torn away from 
the shell inhabited by one of 
these crabs, the crab will wan- 
der about, carefully seeking 
for another anemone. When 
he finds it he struggles to 
loosen it from its rock or 
from whatever it may be growing on, and does not rest 
until he has torn it loose and placed it on his shell. 

There are numerous small crabs called pea-crabs (Pin- 




Fig. 202.— A Portuguese man-of-war 
(Physalia), with man-of-war fishes 
(Nomeus gronovii) living in the 
shelter of the stinging feelers. 
Specimens from off Tampa, Fla. 



338 ANIMAL STUDIES 

notheres) which live habitually inside the shells of living 
mussels. The mussels and the crabs live together in per- 
fect harmony and to their mutual benefit. 




Fig. 203.— Hermit-crab (Pagurus) in shell, wuh a sea-anemone (Adamsia palliata) 
attached to the shell.— After Hertwig. 

272. Relation of parasite and host. — There are many 
instances in the animal kingdom of an association between 
two animals by which one gains advantages great or small, 
sometimes even obtaining all the necessities of life, while 
the other gains nothing, but suffers corresponding dis- 
advantage, often even the loss of life itself. This is the 
association between two animals whereby one, the para- 
site, lives on or in the other, the host, and at the ex- 
pense of the host. Parasitism is a common phenomenon 
in all groups of animals ; but parasites themselves are 
mostly invertebrates. When an animal can get along 
more safely or more easily by living at the expense of 
some other animal and takes up such a life, it becomes a 
parasite. 

273. Kinds of parasitism. — The bird-lice {Mallophaga), 
which infest the bodies of all kinds of birds and are found 



COMMENSALISM AND PARASITISM 339 

especially abundant on domestic fowls, live upon the out- 
side of the bodies of their hosts, feeding upon the feathers 
and dermal scales. They are examples of external parasites. 
Other examples are fleas and ticks, and the crustaceans 
called fish-lice and whale-lice, which are attached to marine 
animals. On the other hand, almost all animals are infested 
by certain parasitic worms which live in the alimentary 
canal, like the tape-worm, or imbedded in the muscles, like 
the trichina. These are examples of internal parasites. 
Such parasites belong mostly to the class of worms, and 
some of them are very injurious, sucking the blood from 
the tissues of the host, while others feed solely on the partly 
digested food. There are also parasites that live partly 
within and partly on the outside of the body, like the Sac- 
culina, which lives on various kinds of crabs. The body of 
the Sacculina consists of a soft sac which lies on the outside 
of the crab's body, and of a number of long, slender root- 
like processes, which penetrate deeply into the crab's body, 
and take up nourishment from within. The Sacculina i3 
itself a crustacean or crab-like creature. The classification 
of parasites as external and internal is purely arbitrary, but 
it is often a matter of convenience. 

Some parasites live for their whole lifetime on or in the 
body of the host, as is the case with the bird-lice. Their 
eggs are laid on the feathers of the bird host ; the young 
when hatched remain on the bird during growth and devel- 
opment, and the adults only rarely leave the body, usually 
never. These may be called permanent parasites. On the 
other hand, fleas leap off or on a dog as caprice dictates ; 
or, as in other cases, the parasite may pass some definite 
part of its life as a free, non-parasitic organism, attaching 
itself, after development, to some animal, and remaining 
there for the rest of its life. These parasites may be called 
temporary parasites. But this grouping or classification, 
like that of the external or internal parasites, is simply 
a matter of convenience, and does not indicate at all 



340 ANIMAL STUDIES 

any blood relationship among the members of any one 
group. 

274. The simple structure of parasites. — In all cases the 
body of a parasite is simpler in structure than the body of 
other animals which are closely related to the parasite — 
that is, animals that live parasitically have simpler bodies 
than animals that live free, active lives, competing for 
food with the other animals about them. This simplicity 
is not primitive, but results from the loss or atrophy of the 
structures which the mode of life renders useless. Many 
parasites are attached firmly to their host, and do not move 
about. They have no need of the power of locomotion. 
They are carried by their host. Such parasites are usually 
without wings, legs, or other locomotory organs. Because 
they have given up locomotion they have no need of or- 
gans of orientation, those special sense organs like eyes 
and ears and feelers, which serve to guide and direct the 
moving animal ; and most non-locomotory parasites will be 
found to have no eyes, nor any of the organs of special 
sense which are accessory to locomotion and which serve 
for the detection of food or of enemies. Because these im- 
portant organs, which depend for their successful activity 
on a highly organized nervous system, are lacking, the 
nervous system of parasites is usually very simple and un- 
developed. Again, because the parasite usually has for 
its sustenance the already digested highly nutritious food 
elaborated by its host, most parasites have a very simple 
alimentary canal, or even no alimentary canal at all. 
Finally, as the fixed parasite leads a wholly sedentary and 
inactive life, the breaking down and rebuilding of tissue in 
its body go on very slowly and in minimum degree, and 
there is no need of highly developed respiratory and circu- 
latory organs ; so that 'most fixed parasites have these sys- 
tems of organs in simple condition. They often bear no 
resemblance to the complex forms from which they are 
descended. 



COMMENSALISM AND PARASITISM 



341 



275. Sacculina. — Among the more highly organized ani- 
mals the results of a parasitic life, in degree of structural 
degeneration, can be more readily seen. A well-known para- 
site, belonging to the Crustacea — the class of shrimps, crabs, 
lobsters, and cray-fishes — is Sacculina. The young Sac- 
culina is an active, free-swimming larva much like a young 
prawn or young crab. But the adult bears absolutely no 
resemblance to 
such a typical 
crustacean as a 
cray-fish or crab. 
The Sacculina, 
after a short 
period of inde- 
pendent exist- 
ence, attaches 
itself to the ab- 
domen of a crab, 
and there com- 
pletes its devel- 
opment while 
living as a parasite. In its adult condition (Fig. 204) it is 
simply a great tumor-like sac, bearing many delicate, root- 
like suckers, which penetrate the body of the crab host and 
absorb nutriment. The Sacculina has no eyes, no mouth 
parts, no legs, or other appendages, and hardly any of the 
usual organs except reproductive organs. Degeneration here 
is carried very far. 

276. Parasitic insects. — In the order Hymenoptera there 
are several families, all of whose members live during their 
larval stage as parasites. We may call all these hymen- 
opterous parasites ichneumon flies. The ichneumon flies 
are parasites of other insects, especially of the larvae of 
beetles and moths and butterflies. In fact, the ichneumon 
flies do more to keep in check the increase of injurious and 
destructive caterpillars than do all our artificial remedies 




Fig. 204. — Sacculina, a crustacean parasite of crabs, a. at- 
tached to a crab, with root-like processes penetrating the 
crab's body ; b, removed from the crab. 



342 ANIMAL STUDIES 

for these insect pests. The adult ichneumon fly is four- 
winged and lives an active, independent life. It lays its 
eggs either in or on or near some caterpillar or beetle grub, 
and the young ichneumon, when hatched, burrows about in 
the body of its host, feeding on its tissues, but not attacking 
such organs as the heart or nervous ganglia, whose injury 




Fig. 205.— Parasitized caterpillar from which the ichneumon fly parasites have 
issued, showing the circular holes of exit in the skin. 

would mean immediate death to the host. The caterpillar 
lives with the ichneumon grub within it, usually until 
nearly time for its pupation. In many instances, indeed, 
it pupates, with the parasite still feeding within its body, 
but it never comes to maturity. The larval ichneumon fly 
pupates either within the body of its host (Fig. 205) or 
in a tiny silken cocoon outside of its body. From the 
cocoons the adult winged ichneumon flies emerge, and 
after mating find another host on whose body to lay their 
eggs. 

One of the most interesting ichneumon flies is Thalessa 
(Fig. 209), which has a remarkably long, slender, flexible 
ovipositor, or egg-laying organ. An insect known as the 
pigeon horn-tail (Tremex columha) (Fig. 207) deposits its 
eggs, by means of a strong, piercing ovipositor, half an inch 
deep in the trunk wood of growing trees. The young or 
larval Tremex is a soft-bodied white grub, which bores 
deeply into the trunk of the tree, filling up the burrow be- 
hind it with small chips. The Thalessa is a parasite of the 
Tremex, and when a female Thalessa finds a tree infested 
by Tremex, she selects a place which she judges is opposite 



COMMENSALISM AND PARASITISM 343 

a Tremex burrow, and, elevating her long ovipositor in a 
loop over her back, with its tip on the bark of the tree (Fig. 
208), she makes a derrick out of her body and proceeds with 




Fig. 206.— The adult ichneumon fly. The lines indicate natural dimensions. 

great skill and precision to drill a hole into the tree. When 
the Tremex burrow is reached she deposits an egg in it. 
The larva that hatches from this egg creeps along this 
burrow until it reaches its victim, and then fastens itself to 
the horn-tail larva, which it destroys by sucking its blood. 
The larva of Thalessa, when full grown, changes to a pupa 
within the burrow of its host, and the adult gnaws a hole 
out through the bark if it does not find the hole already 
made by the Tremex. 

277. Degeneration through quiescence.— If for any other 
reason animals should become fixed, and live inactive or 
sedentary lives, they would degenerate. And there are not 
a few instances of degeneration due simply to a quiescent 
life, unaccompanied by parasitism. The Tunicata, or sea- 
squirts (Fig. 210), are animals which have become simple 
through degeneration, due to the adoption of a sedentary 



344 



ANIMAL STUDIES 



life, the withdrawal from the crowd of animals and from 
the struggle which it necessitates. The young tunicate is 




Fig. 208.— Thalessa lunator boring.— After 

COMSTOCK. 



Fig. 209.— The large ichneumon 
Thalessa, with long flexible oviposi- 
tor. The various parts of this ovi- 
positor are spread apart in the fig- 
ure ; naturally they he together to 
form a single piercing organ. 



a free-swimming, active, tad- 
pole-like or fish-like creature, 
which possesses organs very like those of the adult of the 
simplest fishes or fish-like forms. That is, the sea-squirt 



COMMEXSALISM AND PARASITISM 



345 



begins life as a primitively simple vertebrate. It possesses 
in its larval stage a note-chord, the delicate structure which 
precedes the formation of a backbone, extending along the 

upper part of the body, 
below the spinal cord. It 
is found in all young ver- 
tebrates, and is charac- 
teristic of the class. The 
other organs of the young 
tunicate are all of verte- 
bral type. But the young 
sea-squirt passes a period 
of active and free life as 
a little fish, after which 
it settles down and at- 
taches itself to a stone or 
shell or wooden pier by 
means of suckers, and re- 
mains for the rest of its 
life fixed. Instead of go- 
ing on and developing 
into a fish-like creature, it 
loses its notochord, its 
special sense organs, and 
other organs ; it loses its complexity and high organiza- 
tion, and becomes a " mere rooted bag with a double neck," 
a thoroughly degenerate animal. 

A barnacle is another example of degeneration through 
quiescence. The barnacles are crustaceans related most 
nearly to the crabs and shrimps. The young barnacle just 
from the egg (Fig. 211,/) is a six-legged, free-swimming 
nauplius, very like a young prawn or crab, with single eye. 
In its next larval stage it has six pairs of swimming feet, 
two compound eyes, and two large antennae or feelers, and 
still lives an independent, free-swimming life. When it 
makes its final change to the adult condition, it attaches 
23 




Fig. 210.— A sea-squirt, or tunicate. 



346 



ANIMAL STUDIES 



itself to some stone or shell, or pile or ship's bottom, loses 
its compound eyes and feelers, develops a protecting shell, 
and gives up all power of locomotion. Its swimming feet 
become changed into grasping organs, and it loses most of 
its outward resemblances to the other members of its class 
(Fig. 211, e). 




Fig. 211.— Three adult crustacean and their larvae, a, prawn (Peneus), active and 
free-living ; b, larva of prawn ; c, Saccidina, parasite ; d, larva of Sacculina ; 
e, barnacle (Lepas), with fixed quiescent life ; /, larva of barnacle.— After 
Haeckel. 

Certain insects live sedentary or fixed lives. All the 
members of the family of scale insects (Coccidae), in one 
sex at least, show degeneration, that has been caused by 
quiescence. One of these coccids, called the red orange 
scale (Fig. 211), is very abundant in Florida and California 
and in other orange-growing regions. The male is a beau- 
tiful, tiny, two-winged midge, but the female is a wingless, 



COMMENSALISM AND PARASITISM 



347 



footless little sac without eyes or other organs of special 
sense, which lies motionless under a flat, thin, circular, red- 
dish scale composed of wax and two or three cast skins of 
the insect itself. The insect has a long, slender, flexible, 
sucking beak, which is thrust into the leaf or stem or fruit 
of the orange on which the " scale bug " lives and through 
which the insect sucks the orange sap, which is its only 




Fig. 212 — The red orange scale of California, a, bit of leaf with scales ; b, adult 
female ; c, was scale under which adult female lives ; d, larva ; e, adult male. 

food. It lays eggs under its body, and thus also under the 
protecting wax scale, and dies. From the eggs hatch active 
little larval scale-bugs with eyes and feelers and six legs. 
They crawl from under the wax scale and roam about over 
the orange tree. Finally, they settle down, thrusting their 
sucking beak into the plant tissues, and cast their skin. 
The females lose at this molt their legs and eyes and 



848 ANIMAL STUDIES 

feelers. Each becomes a mere motionless sac capable only 
of sucking up sap and of laying eggs. The young males, 
however, lose their sucking beak and can no longer take 
food, but they gain a pair of wings and an additional pair 
of • eyes. They fly about and fertilize the sac-like females, 
which then molt again and secrete the thin wax scale over 
them. 

Throughout the animal kingdom loss of the need of 
movement is followed by the loss of the power to move, and 
of all structures related to it. 

278. Degeneration through other causes. — Loss of certain 
organs, may occur through other causes than parasitism and 
a fixed life. Many insects live but a short time in their 
adult stage. May-flies live for but a few hours or, at most, 
a few days. They do not need to take food to sustain life 
for so short a time, and so their mouth parts have become 
rudimentary and functionless or are entirely lost. This is 
true of some moths and numerous other specially short- 
lived insects. Among the social insects the workers of the 
termites and of the true ants are wingless, although they 
are born of winged parents, and are descendants of winged 
ancestors. The modification of structure dependent upon 
the division of labor among the individuals of the com- 
munity has taken the form, in the case of the workers, of a 
degeneration in the loss of the wings. Insects that live 
in caves are mostly blind ; they have lost the eyes, whose 
function could not be exercised in the darkness of the cave. 
Certain island-inhabiting insects have lost their wings, 
flight being attended with too much danger. The strong 
sea-breezes may at any time carry a flying insect off the 
small island to sea. Only those which do not fly much sur- 
vive, and by natural selection wingless breeds or species are 
produced. Finally, we may mention the great modifications 
of structure, often resulting in the loss of certain organs, 
which take place to produce protective resemblances (see 
Chapter XXIV). In such cases the body may be modified 



COMMENSALISM AND PARASITISM 349 

in color and shape so as to resemble some part of the envi- 
ronment, and thus the animal may be unperceived by its 
enemies. Many insects have lost their wings through this 
cause. 

279. Immediate causes of degeneration. — When we say 
that a parasitic or quiescent mode of life leads to or causes 
degeneration, we have explained the stimulus or the ulti- 
mate cause of degenerative changes, but we have not 
shown just how parasitism or quiescence actually produces 
these changes. Degeneration or the atrophy and disap- 
pearance of organs or parts of a body is often said to be 
due to disuse. That is, the disuse of a part is believed by 
many naturalists to be the sufficient cause for its gradual 
dwindling and final loss. That disuse can so affect parts 
of a body during the lifetime of an individual is true. A 
muscle unused becomes soft and flabby and small. Whether 
the effects of such disuse can be inherited, however, is open 
to serious doubt. If not, some other immediate cause, or 
some other cause along with disuse, must be found. Such 
a cause must be sought for in the action of natural selec- 
tion, preserving the advantages of simplicity of structure 
where action is not required. 



CHAPTEE XXIV 

PROTECTIVE RESEMBLANCES, AND MIMICRY 

280. Protective resemblance defined. — If a grasshopper 
be startled from the ground, you may watch it and deter- 
mine exactly where it alights after its leap or flight, and 
yet, on going to the spot, be wholly unable to find it. The 
colors and marking of the insect so harmonize with its sur- 
roundings of soil and vegetation that it is nearly indistin- 
guishable as long as it remains at rest. And if you were 
intent on capturing grasshoppers for fish-bait, this resem- 
blance in appearance to their surroundings would be very 
annoying to you, while it would be a great advantage to 
the grasshoppers, protecting some of them from capture and 
death. This is protective resemblance. Mere casual obser- 
vation reveals to us that such instances of protective resem- 
blance are very common among animals. A rabbit or grouse 
crouching close to the ground and remaining motionless 
is almost indistinguishable. Green caterpillars lying out- 
stretched along green grass-blades or on green leaves may 
be touched before being recognized by sight. In arctic 
regions of perpetual snow the polar bears, the snowy arctic 
foxes, and the hares are all pure white instead of brown 
and red and gray like their cousins of temperate and warm 
regions. Animals of the desert are almost without excep- 
tion obscurely mottled with gray and sand color, so as to 
harmonize with their surroundings. 

In the struggle for existence anything that may give 
an animal an advantage, however slight, may be sufficient 
to turn the scale in favor of the organism possessing the 
350 



PROTECTIVE RESEMBLANCES, AND MIMICRY 351 

advantage. Such an advantage may be swiftness of move- 
ment, or unusual strength or capacity to withstand unfa- 
vorable meteorological conditions, or the possession of such 
color and markings or peculiar shape as tend to conceal the 
animal from its enemies or from its prey. Eesemblances 
may serve the purpose of aggression as well as protection. 
In the case of the polar bears and other predaceous ani- 
mals that show color likenesses to their surroundings, the 
resemblance can better be called aggressive than protective. 
The concealment afforded by the resemblance allows them 
to steal unperceived on their prey. This, of course, is an 
advantage to them as truly as escape from enemies would be. 

We have already seen that by the action of natural 
selection and heredity those variations or conditions that 
give animals advantages in the struggle for life are pre- 
served and emphasized. And so it has come about that 
advantageous protective resemblances are very widespread 
among animals, and assume in many cases extraordinarily 
striking and interesting forms. In fact, the explanation 
of much of the coloring and patterning of animals depends 
on this principle of protective resemblance. 

Before considering further the general conditions of 
protective resemblances, it will be advisable to refer to 
specific examples classified roughly into groups or special 
kinds of advantageous colorings and markings. 

281. General protective or aggressive resemblance. — As 
examples of general protective resemblance — that is, a gen- 
eral color effect harmonizing with the usual surroundings 
and tending to hide or render indistinguishable the animal 
— may be mentioned the hue of the green parrots of the 
evergreen tropical forests ; of the green tree-frogs and tree- 
snakes which live habitually in the green foliage ; of the 
mottled gray and tawny lizards, birds, and small mam- 
mals of the deserts ; and of the white hares and foxes 
and snowy owls and ptarmigans of the snow-covered arc- 
tic regions. Of the same nature is the slaty blue of the 



352 ANIMAL STUDIES 

gulls and terns, colored like the sea. In the brooks most 
fishes are dark olive or greenish above and white below. 
To the birds and other enemies which look down on them 
from above they are colored like the bottom. To their fish 
enemies which look up from below, their color is like the 
white light above them, and their forms are not clearly 
seen. The fishes of the deep sea in perpetual darkness are 




Fig. 213.— Alligator lizard (Gerrhonotus scincicauda) on granite rock. Photograph 
by J. 0. Snyder, Stanford University, California. 

inky violet in color below as well as above. Those that 
live among sea-weeds are red, grass-green, or olive, like 
the plants they frequent. General protective resemblance 
is very widespread among animals, and is not easily appre- 
ciated when the animal is seen in museums or zoological 
gardens — that is, away from its natural or normal environ- 
ment. A modification of general color resemblance found 
in many animals may be called variable protective resem- 
blance. Certain hares and other animals that live in 
northern latitudes are wholly white during the winter when 
the snow covers everything, but in summer, when much of 
the snow melts, revealing the brown and gray rocks and 



PROTECTIVE RESEMBLANCES, AND MIMICRY 353 



withered leaves, these creatures change color, putting on 
a grayish and brownish coat of hair. The ptarmigan of 
the Eocky Mountains (one of the grouse), which lives on 
the snow and rocks of the high peaks, is almost wholly 
white in winter, but in summer when most of the snow is 
melted its plumage is chiefly brown. On the campus at 
Stanford University there is a little pond whose shores are 
covered in some places with bits of bluish rock, in other 
places with bits of reddish rock, and in still other places 
with sand. A small insect called the toad-bug ( Galgulus 
oculatus) lives abundantly on the banks of this pond. 
Specimens collected from the blue rocks are bluish in 
color, those from the red rocks are reddish, and those from 
the sand are sand-colored. Such changes of color to suit 
the changing surroundings can be quickly made in the case 
of some animals. The chameleons of the tropics, whose 
skin changes color momentarily from green to brown, 
blackish or golden, is an excellent example of this highly 
specialized condition. The same change is shown by a 
small lizard of our Southern States (Anolius), which from its 
habit is called the Florida 
chameleon. There is a lit- 
tle fish {Oligocottus snyderi) 
which is common in the tide 
pools of the bay of Monterey, 
in California, whose color 
changes quickly to harmo- 
nize with the different colors 
of the rocks it happens to 
rest above. Some of the tree- 
frogs show this variable col- 
oring. A very striking in- 
stance of variable protective 
resemblance is shown by the 
chrysalids of certain butterflies. An eminent English nat- 
uralist collected many caterpillars of a certain species of 




Fig. 214.— Chry s=ali d of swallow-tail but- 
terfly (Papilio), harmonizing with the 
bark on which it rests. 



354 ANIMAL STUDIES 

butterfly, and put them, just as they were about to change 
into pup® or chrysalids, into various boxes, lined with paper 
of different colors. The color of the chrysalid was found 



; 



Pig. J!5.-Chrysalia of butterfly (lower Jeft-hand projection from stem), showing pro- 
tective resemblance. Photograph from Nature. 

to harmonize very plainly with the color of the lining of 
the box in which the chrysalid hung. It is a familiar fact 
to entomologists that most butterfly chrysalids resemble in 



PROTECTIVE RESEMBLANCES, AND MIMICRY 355 

color and general external appearance the surface of the 
object on which they rest (Figs. 214 and 215). 

282. Special protective resemblance. — Far more striking 
are those cases of protective resemblance in which the ani- 
mal resembles in color and shape, sometimes in extraor- 
dinary detail, some particular object or part of its usual 
environment. Certain parts of the Atlantic Ocean are 
covered with great patches of sea-weed called the gulf-weed 
(Sargassum), and many kinds of animals — fishes and other 
creatures — live upon and among the algae. Xo one can fail 
to note the extraordinary color resemblances which exist 
between those animals and the weed itself. The gulf-weed 
is of an olive-yellow color, and the crabs and shrimps, a cer- 
tain fiat-worm, a certain mollusk, and a little fish, all of 
which live among the Sargassum, are exactly of the same 
shade of yellow as the weed, and have small white markings 
on their bodies which are characteristic also of the Sargas- 
sum. The mouse-fish or Sargassum. fish and the little sea- 
horses, often attached to the gulf-weed, show the same 
traits of coloration. In the black rocks about Tahiti is 
found the black noki or lava-fish {Emmydriclithys vul- 
canus) (Fig. 167), which corresponds perfectly in color and 
form to a piece of lava. This fish is also noteworthy for 
having envenomed spines in the fin on its back. The . 
slender grass-green caterpillars of many moths and butter- 
flies resemble very closely the thin grass-blades among 
which they live. The larvae of the geometrid moths, called 
inch-worms or span-worms, are twig-like in appearance, 
and have the habit, when disturbed, of standing out stiffly 
from the twig or branch upon which they rest, so as to re- 
semble in position as well as in color and markings a short 
or a broken twig. One of the most striking resemblances 
of this sort is shown by the large geometrid larva illus- 
trated in Fig. 216, which was found near Ithaca, Xew York. 
The body of this caterpillar has a few small, irregular spots 
or humps, resembling very exactly the scars left by fallen 



356 



ANIMAL STUDIES 



buds or twigs. These caterpillars have a special muscular 
development to enable them to hold themselves rigidly for 




Fig. 216.— A geometric! larva on a branch. (The 
larva is the upper right-hand projection from 
the stem.) 



Fig. "217.— A walking-stick insect 
{Diapheromera femorata) on 

twig. 



long times in this trying attitude. They also lack the 
middle prop-legs of the body, common to other lepidopter- 



PROTECTIVE RESEMBLANCES, AND MIMICRY 357 



ous larvae, the presence of which would tend to destroy the 
illusion so successfully carried out by them. The common 
walking-stick (Diap7ieromera) (Fig. 217), with its wingless, 
greatly elongate, dull-colored body, is an excellent example 
of special protective resemblance. It is quite indistinguish- 
able, when at rest, from the twigs to which it is clinging. 
Another member of the family of insects to which the walk- 
ing-stick belongs is the famous green-leaf insect (Phyllium) 

(Fig. 218). It is found in 
South America and is of a 
bright green color, with broad 
leaf-like wings and body, with 
markings which imitate the 
leaf veins, and small irregu- 
lar yellowish spots which 
mimic decaying or stained 
or fungus-covered spots in 
the leaf. 

There are many butter- 
flies that resemble dead 
leaves. All our common 
meadow browns (Grapta), 
brown and reddish butter- 
flies with ragged-edged wings, 
that appear in the autumn 
and flutter aimlessly about ex- 
actly like the falling leaves, 
show this resemblance. But 
most remarkable of all is a 
large butterfly {Kallima) (Fig. 219) of the East Indian 
region. The upper sides of the wings are dark, with 
purplish and orange markings, not at all resembling a 
dead leaf. But the butterflies when at rest hold their 
wings together over the back, so that only the under sides 
of the wings are exposed. The under sides of Kattima's 
wings are exactly the color of a dead and dried leaf, and 




Fig. 218.— The green-leaf insect 
(Phyllium). 



358 



ANIMAL STUDIES 



the wings are so held that all combine to mimic with ex- 
traordinary fidelity a dead leaf still attached to the twig by 
a short pedicle or leaf -stalk imitated by a short tail on the 




Fig. 219.— Kallima, the " dead-leaf butterfly." 

hind wings, and showing midrib, oblique veins, and, most 
remarkable of all, two apparent holes, like those made in 
leaves by insects, but in the butterfly imitated by two small 
circular spots free from scales and hence clear and trans- 



PROTECTIVE RESEMBLANCES, AND MIMICRY 359 

parent. With the head and feelers concealed beneath the 
wings, it makes the resemblance wonderfully exact. 

There are numerous instances of special protective 
resemblance among spiders. Many spiders (Fig. 220) that 





Fig. 220.— Spiders showing unusual shapes and patterns, for purposes of 
aggressive resemblance. 

live habitually on tree trunks resemble bits of bark or small, 
irregular masses of lichen. A whole family of spiders, 
which live in flower-cups lying in wait for insects, are white 
and pink and party-colored, resembling the markings of the 
special flowers frequented by them. This is, of course, a 




Fig. 221.— A pipe-fish (Phyllopteryx) resembling sea-weed, in which it lives. 



special resemblance not so much for protection as for ag- 
gression ; the insects coming to visit the flowers are unable 
to distinguish the spiders and fall an easy prey to them. 

283. Warning colors and terrifying appearances. — In the 
cases of advantageous coloring and patterning so far dis- 



360 ANIMAL STUDIES 

cussed the advantage to the animal lies in the resemblance 
between the animals and their surroundings, in the incon- 
spicuousness and concealment afforded by the coloration. 
But there is another interesting phase of advantageous 
coloration in which the advantage derived is in render- 
ing the animals as conspicuous and as readily recogniz- 
able as possible. While many animals are very inconspicu- 
ously colored, or are manifestly colored so as to resemble 
their surroundings, generally or specifically, many other 
animals are very brightly and conspicuously colored and 
patterned. If we are struck by the numerous cases of imi- 
tative coloring among insects, we must be no less impressed 
by the many cases of bizarre and conspicuous coloration 
among them. 

Many animals, as we well know, possess special and 
effective weapons of defense, as the poison-fangs of the 
venomous snakes and the stings of bees and wasps. Other 
animals, and with these cases most of us are not so well 
acquainted, possess a means of defense, or rather safety, in 
being inedible — that is, in possessing some acrid or ill- 
tasting substance in the body which renders them unpala- 
table to predaceous animals. Many caterpillars have been 
found, by observation in Xature and by experiment, to be 
distasteful to insectivorous birds. Now, it is obvious that 
it would be a great advantage to these caterpillars if they 
could be readily recognized by birds, for a severe stroke by 
a bird's bill is about as fatal to a caterpillar as being wholly 
eaten. Its soft, distended body suffers mortal hurt if cut 
or bitten by the bird's beak. This advantage of being 
readily recognizable is possessed by many if not all ill- 
tasting caterpillars by being brilliantly and conspicuously 
colored and marked. Such colors and markings are called 
warning colors. They are intended to inform birds of the 
fact that the caterpillar displaying them is an ill-tasting 
insect, a caterpillar to be let alone. The conspicuously 
black-and-yellow banded larva (Fig. 147, h) of the common 



PROTECTIVE RESEMBLANCES, AND MIMICRY 361 

Monarch butterfly is a good example of the possession of 
warning colors by distasteful caterpillars.' 

These warning colors are possessed not only by the ill- 
tasting caterpillars, but by many animals which have spe- 
cial means of defense. The wasps and bees, provided with 
stings — dangerous animals to trouble — are almost all con- 
spicuously marked with yellow and black. The lady-bird 
beetles (Fig. 222), composing a whole family of small beetles 





Fig. 222.— Two lady-bird beetles, conspicuously colored and marked. 

which are all ill-tasting, are brightly and conspicuously col- 
ored and spotted. The Gila monster {Heloderma), the only 
poisonous lizard, differs from most other lizards in being 
strikingly patterned with black and brown. Some of the 
venomous snakes are conspicuously colored, as the coral 
snakes (Elaps) or coralillos of the tropics. The naturalist 
Belt, whose observations in Nicaragua have added much to 
our knowledge of tropical animals, describes as follows an 
interesting example of warning colors in a species of frog : 
'•'In the woods around Santo Domingo (Nicaragua) there 
are many frogs. Some are green or brown and imitate 
green or dead leaves, and live among foliage. Others are 
dull earth-colored, and hide in holes or under logs. All 
these come out only at night to feed, and they are all 
preyed upon by snakes and birds. In contrast with these 
obscurely colored species, another little frog hops about in 
24 



362- 



ANIMAL STUDIES 



the daytime, dressed in a bright livery of red and blue. 
He can not be mistaken for any other, and his naming 
breast and blue stockings show that he does not court con- 
cealment. He is very abundant in the damp woods, and I 
was convinced he was uneatable so soon as I made his 
acquaintance and saw the happy sense of security with 
which he hopped about. I took a few specimens home 
with me, and tried my fowls and ducks with them, but 
none would touch them. At last, by throwing down pieces 
of meat, for which there was a great competition among 
them, I managed to entice a young duck into snatching up 
one of the little frogs. Instead of swallowing it, however, 
it instantly threw it out of its mouth, and went about jerk- 
ing its head, as if trying to throw off some unpleasant 
taste." 

Certain animals which are without special means of 
defense and are not at all formidable or dangerous are yet 
so marked or shaped and so behave as to present a threat- 
ening or terrifying appearance. The large green caterpil- 
lars (Fig. 223) of the Sphinx moths — the tomato-worm is a 
familiar one of these larvae — have a formidable-looking, 




Fig. 223.— A " tomato-worm m larva of the Sphinx moth, Phlegethontius Carolina, 
showing terrifying appearance. 



sharp horn on the back of the next to last body ring. 
When disturbed they lift the hinder part of the body, bear- 
ing the horn, and move it about threateningly. As a mat- 
ter of fact, the horn is not at all a weapon of defense, but is 
quite harmless. Numerous insects when disturbed lift 
the hind part of the body, and by making threatening mo- 



PROTECTIVE RESEMBLANCES, AND MIMICRY 363 



tions lead enemies to believe that they possess a sting. 
The striking eye-spots of many insects are believed by some 
entomologists to be of the nature of terrifying appearances. 
The larva (Fig. 224) of the Puss moth (Centra) has been 
often referred to as a striking example of terrifying appear- 
ances. When one of these larvae is disturbed, " it retracts 

its head into the 
first body ring in- 
flating the mar- 
gin, which is of a 
bright red color. 
There are two in- 
tensely black spots 
on this margin in the 
appropriate position for 
eyes, and the whole ap- 
pearance is that of a large 
flat face extending to the 
outer edge of the red mar- 
gin. The effect is an in- 
tensely exaggerated cari- 
cature of a vertebrate 
face, which is probably 
alarming to the verte- 
brate enemies of the cat- 
erpillar. . . . The effect is also greatly strengthened by two 
pink whips which are swiftly protruded from the prongs 
of the fork in which the body terminates. . . . The end 
of the body is at the same time curved forward over the 
back, so that the pink filaments are brandished above the 
head." 

284. Alluring coloration. — A few animals show what are 
called alluring colors — that is, they display a color pattern 
so arranged as to resemble or mimic a flower or other lure, 
and thus to entice to them other animals, their natural prey. 
This is a special kind of aggressive resemblance. A species 




Fig. 224.— Larva of the Pass moth (Cerura). 
Upper figure shows the larva as it appears 
when undisturbed ; lower figure, when dis- 
turbed. — After Poitlton. 



364: ANIMAL STUDIES 

of predatory insect called a " praying-horse " (allied to the 
genus Mantis), found in India, has the shape and color of 
an orchid. Small insects are attracted and fall a prey to it. 
Certain Brazilian fly-catching birds have a brilliantly colored 
crest which can be displayed in the shape of a flower-cup. 
The insects attracted by the apparent flower furnish the fly- 
catcher with food. An Asiatic lizard is wholly colored like 
the sand upon which it lives except for a peculiar red fold 
of skin at each angle of the mouth. This fold is arranged 
in flower-like shape, " exactly resembling a little red flower 
which grows in the sand." Insects attracted by these 
flowers find out their mistake too late. In the tribe of 
fishes called the " anglers " or fishing frogs the front rays 
of the dorsal fin are prolonged in shape of long, slender fila- 
ments, the foremost and longest of which has a flattened 
and divided extremity like the bait on a hook. The fish 
conceals itself in the mud or in the cavities of a coral reef 
and waves the filaments back and forth. Small fish are at- 
tracted by the lure, mistaking it for worms writhing about 
in the water or among the weeds. As they approach they 
are ingulfed in the mouth of the angler, which in some of 
the species is of enormous size. One of these species is 
known to fishermen as the "all-mouth." These fishes 
(Lophius piscatorius), which live in the mud, are colored 
like mud or clay. Other forms of anglers, living among 
coral reefs, are brown and red (Antennarius), their colora- 
tion imitating in minutest detail the markings and out- 
growths on the reef itself, the lure itself imitating a worm 
of the reef. In a certain group of deep-sea anglers, the sea- 
devils {Ceratiidce), certain species show a still further spe- 
cialization of the curious fishing-rod. In one species (Co- 
rynolophus reinhardti) (Fig. 156), living off the coast of 
Greenland at a depth of upward of a mile, the fishing-rod 
or first dorsal spine has a luminous bulb at its tip around 
which are fleshy, worm-like streamers. At the abyssal 
depths of a mile, more or less, frequented by these sea- 



PROTECTIVE RESEMBLANCES, AND MIMICRY 365 

devils there is no light, the inky darkness being absolute. 
This shining lure is therefore a most effective means of 
securing food. 

285. Mimicry. — Although the word mimicry could often 
have been used aptly in the foregoing account of protective 
resemblances, it has been reserved for use in connection 
with a certain specific group of cases. It has been reserved 
to be applied exclusively to those rather numerous instances 
where an otherwise defenseless animal, one without poison- 
fangs or sting, and without an ill-tasting substance in its 
body, mimics some other specially defended or inedible ani- 
mal sufficiently to be mistaken for it and so to escape 
attack. Such cases of protective resemblance are called 
true mimicry, and they are especially to be observed among 
insects. 

In Fig. 225 are pictured three familiar American butter- 
flies. One of these, the Monarch butterfly (Anosia plexip- 
pus), is perhaps the most abundant and widespread butter- 
fly of our country. It is a fact well known to entomologists 
that the Monarch is distasteful to birds and is let alone by 
them. It is a conspicuous butterfly, being large and chiefly 
of a red-brown color. The Viceroy butterfly (Basilarchia 
archippus), also red-brown and much like the Monarch, is 
not, as its appearance would seem to indicate, a very near 
relative of the Monarch, belonging to the same genus, but 
on the contrary it belongs to the same genus with the third 
butterfly figured, the black and white Basilarchia. All the 
butterflies of the genus Basilarchia are black and white 
except this species, the Viceroy, and one other. The Vice- 
roy is not distasteful to birds ; it is edible, but it mimics the 
inedible Monarch so closely that the deception is not de- * 
tected by the birds, and so it is not molested. 

In the tropics there have been discovered numerous 
similar instances of mimicry by edible butterflies of inedi- 
ble kinds. The members of two great families of butterflies 
(Danaidas and Heliconidae) are distasteful to birds, and are 




iTiG. 225 —The mimicking of the inedible Monarch butterfly by the edible Viceroy. 
Upper figure is the Monarch (Anosia plexippus) ; middle figure is the Viceroy 
(Basilarchia archippus) ; lowest figure is another member of the same genus 
(BasUarchia), to show the usual color pattern of the species of the genus. 



PROTECTIVE RESEMBLANCES, AND MIMICRY 367 



mimicked by members of the other butterfly families (espe- 
cially the Pieridae), to which family our common white 
cabbage-butterfly belongs, and by the swallow-tails (Papi- 
lionidae). 

The bees and wasps are protected by their stings. They 
are usually conspicuous, being banded with yellow and black. 
They are mimicked by numerous other insects, especially 
moths and flies, two defenseless kinds of insects. This 
mimicking of bees and wasps by flies is very common, and 
can be observed readily at any flowering shrub. The flower- 
flies (Syrphidae), which, with the bees, visit flowers, can be 
distinguished from the bees only by sharp observing. When 
these bees and flies can be caught and examined in hand, it 
will be found that the flies have but two wings while the 
bees have four. 

A remarkable and interesting case of mimicry among 
insects of different orders is that of certain South Ameri- 
can tree-hoppers (of the family Membracidas, of the order 
Hemiptera), which mimic the famous leaf-cutting ant 
(Sauba) of the Amazons (Fig. 226). These ants have the 
curious habit of cutting off, with their sharp jaws, bits of 

green leaves and carry- 
ing them to their nests. 
In carrying the bits of 
leaves the ants hold them 
vertically above their 
heads. The leaf-hoppers 
mimic the ants and their 
burdens with remarka- 
ble exactitude by having 
the back of the body ele- 
vated in the form of a 
thin, jagged-edged ridge no thicker than a leaf. This part 
of the body is green like the leaves, while the under part 
of the body and the legs are brown like the ants. 

Some examples of mimicry among other animals than 




Fig. 226.— Tree-hopper (Membracidse), which 
mimics the leaf -cutting ant {Sauba) of Bra- 
zil. (Upper right-hand insect is the tree- 
hopper.) 



368 ANIMAL STUDIES 

insects are known, but not many. The conspicuously 
marked venomous coral-snake or coralillos (Elajis) is mim- 
icked by certain non-venomous snakes called king-snakes 
(Lampropeltis, Osceola). The pattern of red and black 
bands surrounding the cylindrical body is perfectly imi- 
tated. But whether this is true mimicry brought about 
for purposes of protection may be doubted. Instances 
among birds have been described, and a single case has 
been recorded in the class of mammals. But it is among 
the insects that the best attested instances occur. The 
simple fact of the close resemblance of two widely related 
animals can not be taken to prove the existence of mimicry. 
Two animals may both come to resemble some particular 
part in their common environment and thus to resemble 
closely each other. Here we have simply two instances 
of special protective resemblance, and not an instance of 
mimicry. The student of zoology will do well to watch 
sharply for examples of protective resemblance or mimicry, 
for but few of the instances that undoubtedly exist are as 
yet known. 

286. Protective resemblances and mimicry most common 
among insects. — The large majority of the preceding exam- 
ples have been taken from among the insects. This is 
explained by the fact that the phenomena of protective 
resemblances and mimicry have been studied especially 
among insects ; the theory of mimicry was worked out 
chiefly from the observation and study of the colors and 
markings of insects and of the economy of insect life. 
Why protective resemblances and mimicry among insects 
have been chiefly studied is because these conditions are 
specially common among insects. The great class Insecta 
includes more than two thirds of all the known living 
species of animals. The struggle for existence among the 
insects is especially severe and bitter. All kinds of " shifts 
for a living " are pushed to extremes ; and as insect colors 
and patterns are especially varied and conspicuous, it is 



PROTECTIVE RESEMBLANCES, AND MIMICRY 369 

only to be expected that this useful modification of colors 
and patterns, that results in the striking phenomena of 
special protective resemblances and mimicry, should be 
specially widespread and pronounced among insects. More- 
over, they are mostly deficient in other means of defense, 
and seem to be the favorite food for many different kinds 
of animals. Protective resemblance is their best and most 
widely adopted means of preserving life. 

287. No volition in mimicry. — The use of the word mim- 
icry has been criticised because it suggests the exercise of 
volition or intent on the part of the mimicking animal. 
The student should not entertain this conception of mim- 
icry. In the use of "mimicry" in connection with the 
phenomena just described, the biologist ascribes to it a 
technical meaning, which excludes any suggestion of voli- 
tion or intent on the part of the mimic. Just how such 
extraordinary and perfect cases of mimicry as shown by 
Phyllium and Kallima have come to exist is a problem 
whose solution is not agreed on by naturalists, but none of 
them makes volition — the will or intent of the animal — any 
part of his proposed solution. Each case of mimicry is the 
result of a slow and gradual change, through a long series 
of ancestors. The mimicry may indeed include the adop- 
tion of certain habits of action which strengthen and make 
more pronounced the deception of shape and color. But 
these habits, too, are the result of a long development, and 
are instinctive or reflex — that is, performed without the 
exercise of volition or reason. 

288. Color ; its utility and beauty.— The causes of color, 
and the uses of color in animals and in plants are subjects 
to which naturalists have paid and are paying much atten- 
tion. The subject of " protective resemblances and mim- 
icry" is only one, though one of the most interesting, 
branches or subordinate subjects of the general theory of 
the uses of color. Other uses are obvious. Bright colors 
and markings may serve for the attraction of mates ; thus 



370 ANIMAL STUDIES 

are explained by some naturalists the brilliant plumage of 
the male birds, as in the case of the bird-of-paradise and 
the pheasants. Or they may serve for recognition charac- 
ters, enabling the individuals of a band of animals readily 
to recognize their companions ; the conspicuous whiteness 
of the short tail of the antelopes and cotton-tail rabbits, 
the black tail of the black-tail deer, and the white tail- 
feathers of the meadow-lark, are explained by many natu- 
ralists on this ground. Eecognition marks of this type 
are especially numerous among the birds, hardly a species 
being without one or more of them, if their meaning is cor- 
rectly interpreted. The white color of arctic animals may 
be useful not alone in rendering them inconspicuous, but 
may serve also a direct physiological function in preventing 
the loss of heat from the body by radiation. And the dark 
colors of animals may be of value to them in absorbing heat 
rays and thus helping them to keep warm. But " by far 
the most widespread use of color is to assist an animal in 
escaping from its enemies or in capturing its prey.'' 

The colors of an animal may indeed not be useful to 
it at all. Many color patterns exist on present-day birds 
simply because, preserved by heredity, they are handed 
down by their ancestors, to whom, under different condi- 
tions of life, they may have been of direct use. For the 
most part, however, we can look on the varied colors and 
the striking patterns exhibited by animals as being in some 
way or another of real use and value. We can enjoy the 
exquisite coloration of the wings of a butterfly none the 
less, however, because we know that these beautiful colors 
and their arrangement tend to preserve the life of the 
dainty creature, and have been produced by the operation 
of fixed laws of Xature working through the ages. 



CHAPTEE XXV 

THE SPECIAL SENSES 

289. Importance of the special senses. — The means by 
■which animals become acquainted with the outer world 
are the special senses, such as feeling, tasting, smelling, 
hearing, and seeing. The behavior of animals with regard 
to their surroundings, with regard to all the world outside 
of their own body, depends upon what they learn of this 
outer world through the exercise of these special senses. 
Habits are formed on the basis of experience or knowledge 
of the outer world gained by the special senses, and the 
development of the power to reason or to have sense de- 
pends on their pre-existence. 

290. Difficulty of the study of the special senses. — We are 
accustomed to think of the organs of the special senses as 
extremely complex parts of the body, and this is certainly 
true in the case of the higher animals. In our own body 
the ears and eyes are organs of most specialized and highly 
developed condition. But we must not overlook the fact 
that the animal kingdom is composed of creatures of widely 
varying degrees of organization, and that in any considera- 
tion of matters common to all animals those animals of 
simplest and most lowly organization must be studied as 
well as those of high development. The study of the spe- 
cial senses presents two phases, namely, the study of the 
structure of the organs of special sense, and the study of 
the physiology of special sense — that is, the functions of 
these organs. It will be recognized that in the study of 
how other animals feel and taste and smell and hear and 

371 



372 ANIMAL STUDIES 

see, we shall have to base all our study on our own experi- 
ence. We know of hearing and seeing only by what we 
know of our own hearing and seeing ; but by examination 
of the structure of the hearing and seeing organs of cer- 
tain other animals, and by observation and experiments, 
zoologists are convinced that some animals hear sounds 
that we can not hear, and some see colors that we can 
not see. 

While that phase of the study of the special senses 
which concerns their structure may be quite successfully 
undertaken, the physiological phase of the study of the 
actual tasting and seeing and hearing of the lower animals 
is a matter of much difficulty. The condition and char- 
acter of the special senses vary notably among different 
animals. There may even exist other special senses than 
the ones we possess. Some zoologists believe that certain 
marine animals possess a " density or pressure sense " — 
that is, a sense which enables them to tell approximately 
how deep in the water they may be at any time. To 
certain animals is ascribed a " temperature sense," and 
some zoologists believe that what we call the homing in- 
stinct of animals as shown by the homing pigeons and 
honey-bees and other animals, depends on their possession 
of a special sense which man does not possess. Recent 
experiments, however, seem to show that the homing of 
pigeons depends on their keen sight. In numerous animals 
there exist, besides the organs of the five special senses 
which we possess, organs whose structure compels us to be- 
lieve them to be organs of special sense, but whose func- 
tion is wholly unknown to us. Thus in the study of the 
special senses we are made to see plainly that we can not 
rely simply on our knowledge of our own body structure 
for an understanding of the structure and functions of 
other animals. 

291. Special senses of the simplest animals. — The Amoeba, 
described in Chapter I of Animal Life, is a one-celled 



THE SPECIAL SENSES 373 

body, without organs, and yet with its capacity for per- 
forming the necessary life processes ; there are no special 
senses except one (perhaps two). The Amoeba can feel. 
It possesses the tactile sense. And there are no special 
sense organs except one, which is the whole of the outer 
surface of the body. If the Amoeba be touched with a 
fine point it feels the touch, for the soft viscous proto- 
plasm of its body flows slowly away from the foreign ob- 
ject. The sense of feeling or touch, the tactile sense, is 
the simplest or most primitive of the special senses, and 
the simplest, most primitive organ of special sense is the 
outer surface or skin of the body. Among those simple 
animals that possess the simplest organs of hearing and 
perceiving light, we shall find these organs to be simply 
specialized parts of the skin or outer cell layer of the 
body, and it is a fact that all the special sense organs of 
all animals are derived or developed from the outer cell 
layer, ectoblast, of the embryo. This is true also of the 
whole nervous system, the brain and spinal cord of the 
vertebrates, and the ganglia and nerve commissures of 
the invertebrates. And while in the higher animals the 
nervous system lies underneath the surface of the body, 
in many of the lower, many-celled animals all the ganglia 
and nerves, all of the nervous system, lie on the outer 
surface of the body, being simply a specialized part of 
the skin. 

292. The sense of touch. — In some of the lower, many- 
celled animals, as among the polyps, there are on the skin 
certain sense cells, either isolated or in small groups, which 
seem to be stimulated not alone by the touching of foreign 
substances, but also by warmth and light. They are not 
limited to a single special sense. They are the primitive 
or generalized organs of special sense, and can develop into 
specialized organs for any one of the special senses. 

The simplest and most widespread of these special 
senses with, as a whole, the simplest organs, is the tactile 



374 



ANIMAL STUDIES 



sense, or the sense of touch. The special organs of this 
sense are usually simple hairs or papillae connecting with a 
nerve. These tactile hairs or papillae may be distributed 
pretty evenly over most of the body, or may be mainly con- 
centrated upon certain parts in crowded groups. Many of 
the lower animals have projecting parts, like the feeling 
tentacles of many marine invertebrates, or the antennae 
(feelers) of crabs and insects, which are the special seat 
of the tactile organs. Among the vertebrates the tactile 
organs are either like those of the invertebrates, or are 
little sac-like bodies of connective tissue in which the 
end of a nerve is curiously folded and convoluted (Fig. 
227). These little touch corpuscles simply lie in the cell 
layer of the skin, covered over thinly by the cuticle. Some- 
times they are simply free, branched 
nerve-endings in the skin. These 
tactile corpuscles or free nerve-end- 
ings are especially abundant in those 
parts of the body which can be best 
used for feeling. In man the fin- 
ger-tips are thus especially supplied ; 
in certain tailed monkeys the tip of 
the tail, and in hogs the end of the 
snout. The difference in abundance 
of these tactile corpuscles of the skin 
can be readily shoAvn by experiment. 
With a pair of compasses, whose 
points have been slightly blunted, 
touch the skin of the forearm of a 

person who has his eyes shut, with the points about three 
inches apart and in the direction of the length of the arm. 
The person touched will feel the points as two. Eepeat 
the touching several times, gradually lessening the dis- 
tance between the points. When the points are not more 
than an inch to an inch and a half apart, the person 
touched will feel but a single touch — that is, the touching 




Fig. 227.— Tactile papilla of 
skin of man. n, nerve. — 
After Koelliker. 



THE SPECIAL SENSES 375 

of both points will give the sensation of but a single con- 
tact. Eepeat the experiment on the tip of the forefinger, 
and both points will be felt until the points are only about 
one tenth of an inch apart. 

293. The sense of taste. — The sense of taste enables us to 
test in some degree the chemical constitution of substances 
which are taken into the mouth as food. We discriminate 
by the taste organs between good food and bad, well-tasting 
and ill-tasting. These organs are, with us and the other air- 
breathing animals, located in the mouth or on the mouth 
parts. They must be located so as to come into contact 
with the food, and it is also necessary that the food sub- 
stance to be tasted be made liquid. This is accomplished 
by the fluids poured into the mouth from the salivary 
glands. With the lower aquatic animals it is not improb- 
able that taste organs are situated on other parts of the 
body besides the mouth, and that taste is used not only to 
test food substances, but also to test the chemical char- 
acter of the fluid medium in which they live. 

The taste organs are much like the tactile organs, ex- 
cept that the special taste cell is exposed, so that small par- 
ticles of the substance to be tasted can come into actual 
contact with it. The nerve-ending is usually in a small 
raised papilla or depressed pit. In the simplest animals 
there is no special organ of taste, and yet Amoeba and 
other Protozoa show that they appreciate the chemical con- 
stitution of the liquid in which they lie. They taste — that 
is, test the chemical constitution of the substances — by 
means of their undifferentiated body surface. The taste 
organs are not always to be told from the organs of smell. 
Where an animal has a certain special seat of smell, like 
the nose of the higher animals, then the special sense 
organs of the mouth can be fairly assumed to be taste 
organs ; but where the seat of both smell and taste is in 
the mouth or mouth parts, it is often impossible to distin- 
guish between the two kinds of organs. 




376 ANIMAL STUDIES 

In mammals taste organs are situated on certain parts of 
the tongue, and have the form of rather large, low, broad 
papilla?, each bearing many small taste-buds (Fig. 228). 
In fishes similar papilla? and buds have been found in vari- 
ous places on the sur- 
face of the body, from x ^ . 
which it is believed that t ^ 
the sense of taste in 
fishes is not limited to 
the mouth. In insects 
the taste - papilla? and 
taste -pits are grouped 

in Certain places On the Fig. 228.— Vertical section of laree papilla on 

mouth parts, being es- ^ ° f a calf; fci - taste " bud8 - " Af ter 
pecially abundant on 

the tips of small, segmented, feeler-like processes called 
palpi, which project from the under lip and from the so- 
called maxilla?. 

294. The sense of smell. — Smelling and tasting are closely 
allied, the one testing substances dissolved, the other test- 
ing substances vaporized. The organs of the sense of 
smell are, like those of taste, simple nerve-endings in papil- 
la? or pits. The substance to be smelled must, however, 
be in a very finely divided form ; it must come to the or- 
gans of smell as a gas or vapor, and not, as to the organs of 
taste, in liquid condition. The organs of smell are situated 
usually on the head, but as the sense of smell is used not 
alone for the testing of food, but for many other purposes, 
the organs of smell are not, like those of taste, situated 
principally in or near the mouth. Smell is a special sense 
of much wider range of use than taste. By smell animals 
can discover food, avoid enemies, and find their mates. 
They can test the air they breathe as well as the food they 
eat. In the matter of the testing of food the senses of 
both taste and smell are constantly used, and are indeed 
intimately associated. 



THE SPECIAL SENSES 



377 



The sense of smell varies a great deal in its degree of 
development in various animals. With the strictly aquatic 
animals — and these include most of the lower invertebrates, 
as the polyps, the star-fishes, sea-urchins, and most of the 
worms and mollusks — the sense of smell is probably but 
little developed. There is little opportunity for a gas or 
vapor to come to these animals, and only as a gas or vapor 
can a substance be smelled. With these animals the sense 
of taste must take the place of the olfactory sense. But 
among the insects, mostly terrestrial animals, there is an 
extraordinary development of the sense of smell. It is in- 
deed probably their principal special sense. Insects must 
depend on smell far more than on sight or hearing for 
the discovery of food, for becoming 
aware of the presence of their enemies 
and of the proximity of their mates 
and companions. The organs of 
smell of insects are situated princi- 
pally on the antennas or feelers, a 
single pair of which is borne on the 
head of every insect (Fig. 229). That 
many insects have an extraordinarily 
keen sense of smell has been shown 
by numerous experiments, and is con- 
stantly proved by well-known habits. 
If a small bit of decaying flesh be in- 
closed in a box so that it is wholly 
concealed, it will nevertheless soon 
be found by the flies and carrion 
beetles that either feed on carrion 
or must always lay their eggs in de- 
caying matter so that their carrion-eating larvae may be 
provided with food. It is believed that ants find their 
way back to their nests by the sense of smell, and that 
they can recognize by scent among hundreds of individ- 
uals taken from various communities the members of their 
25 




Fig. 229.— Antenna of a leaf- 
eating beetle, showing 
smelling-pits on the ex- 
panded terminal segments. 



378 ANIMAL STUDIES 

own community. In the insectary at Cornell University, 
a few years ago, a few females of the beautiful promethea 
moth (Callosamia promethea) were inclosed in a box, 
which was kept inside the insectary building. Xo males 
had been seen about the insectary nor in its immediate 
vicinity, although they had been sought for by collectors. 
A few hours after the beginning of the captivity of the 
female moths there were forty male prometheas fluttering 
about over the glass roof of the insectary. They could not 




Fig. 230.— Promethea moth, male, showing specialized antennae. 

see the females, and yet had discovered their presence in 
the building. The discovery was undoubtedly made by the 
sense of smell. These moths have very elaborately devel- 
oped antennae (Fig. 230), finely branched or feathered, 
affording opportunity for the existence of very many smell- 
ing-pits. 

The keenness of scent of hounds and bird dogs is famil- 
iar to all, although ever a fresh source of astonishment as 
we watch these animals when hunting. TTe recently 
watched a retriever dog select unerringly, by the sense of 
smell, any particular duck out of a pile of a hundred. In 



THE SPECIAL SENSES 379 

the case of man the sense of smell is not nearly so well 
developed as among many of the other vertebrates. This 
inferiority is largely due to degeneration through lessened 
need; for in Indians and primitive races the sense of 
smell is keener and better developed than in civilized 
races. Where man has to make his living by hunting, and 
has to avoid his enemies of jungle and plain, his special 
senses are better developed than where the necessity of 
protection and advantage by means of such keenness of 
scent and hearing is done away with by the arts of civi- 
lization. 

295. The sense of hearing. — Hearing is the perception 
of certain vibrations of bodies. These vibrations give rise 
to waves — sound waves as they are called — which proceed 
from the vibrating body in all directions, and which, com- 
ing to an animal, stimulate the special auditory or hearing 
organs, that transmit this stimulation along the auditory 
nerve to the brain, where it is translated as sound. These 
sound waves come to animals usually through the air, or, 
in the case of aquatic animals, through water, or through 
both air and water. 

The organs of hearing are of very complex structure 
in the case of man and the higher vertebrates. Our ears, 
which are adapted for perceiving or being stimulated by 
vibrations ranging from 16 to 40,000 a second — that is, for 
hearing all those sounds produced by vibrations of a rapid- 
ity not less than 16 to a second nor greater than 40,000 to 
a second — are of such complexity of structure that many 
pages would be required for their description. But among 
the lower or less highly organized animals the ears, or au- 
ditory organs, are much simpler. 

In most animals the auditory organs show the common 
characteristic of being wholly composed of, or having as 
an essential part, a small sac filled with liquid in which 
one or more tiny spherical hard bodies called otoliths are 
held. This auditory sac is formed of or lined internally by 



380 



ANIMAL STUDIES 



auditory cells, specialized nerve cells, which often bear 
delicate vibratile hairs (Fig. 231). Auditory organs of this 
general character are known among the polyps, the worms, 
the crustaceans, and the mollusks. In the common cray- 
fish the " ears " are situated in the basal segment of the 
inner antennae or feelers (Fig. 232). They consist each of 
a small sac filled with liquid in which 
are suspended several grains of sand 
or other hard bodies. The inner 





Fig. 231.— Auditory organ of a mollusk. a, audi- 
tory nerve ; b, outer wall of connective tissue ; 
c, cells with auditory hairs ; d, otolith.— After 
Letdig. 



Fig. 232. — Antenna of 
cray - fish, with audi- 
tory sac at base. — 
After Huxlet. 



surface of the sac is lined with fine auditory hairs. The 
sound waves coming through the air or water outside strike 
against this sac, which lies in a hollow on the upper or 
outer side of the antennas. The sound waves are taken up 
by the contents of the sac and stimulate the fine hairs, 
which in turn give this stimulus to the nerves which run 
from them to the principal auditory nerve and thus to the 
brain of the cray-fish. Among the insects other kinds of 
auditory organs exist. The common locust or grasshopper 



THE SPECIAL SENSES 



381 



has on the upper surface of the first abdominal segment 
a pair of tympana or ear-drums (Fig. 233), composed sim- 
ply of the thinned, tightly stretched chitinous 
cuticle of the body. On the inner surface of this 




FiGo 233.— Grasshopper, showing auditory organ (a. o.) in first segment of abdomen. 
(Wings of one side removed.) 

ear-drum there are a tiny auditory sac, a fine nerve lead- 
ing from it to a small auditory ganglion lying near the 
tympanum, and a large nerve leading from this ganglion 
to one of the larger ganglia situated on the floor of the 




CtO 

Fig. 234.— A cricket, showing auditory organ (a. o.) in fore-leg. 

thorax. In the crickets and katydids, insects related to 
the locusts, the auditory organs or ears are situated in the 
fore-legs (Fig. 234). 

Certain other insects, as the mosquitoes and other midges 



382 



ANIMAL STUDIES 



or gnats, undoubtedly hear by means of numerous delicate 

hairs borne on the antennae. The male mosquitoes (Fig. 

235) have many hundreds of these long, fine antennal hairs, 

and on the sounding of a tuning-fork these hairs have been 

observed to vibrate strongly. In the base of each antenna 

there is a most elaborate organ, 

composed of fine chitinous 

rods, and accompanying nerves 

and nerve cells whose function 

it is to take up and transmit 

through the auditory nerve to 

the brain the stimuli received 

from the external auditory 

hairs. 

296. Sound -making. — The 
sense of hearing enables ani- 
mals not only to hear the 
warning natural sounds of 
storms and falling trees and 
plungiog avalanches, but the 
sounds made by each other. 
Sound-making among animals 
serves to aid in frightening 
away enemies or in warning 
companions of their approach, 
for recognition among mates 

and members of a band or species, for the attracting and 
wooing of mates, and for the interchange of information. 
TVith the cries and roars of mammals, the songs of birds, 
and the shrilling and calling of insects all of us are familiar. 
These are all sounds that can be heard by the human ear. 
But that there are many sounds made by animals that 
we can not hear — that is, that are of too high a pitch for 
our hearing organs to be stimulated by — is believed by nat- 
uralists. Especially is this almost certainly true in the case 
of the insects. The peculiar sound-producing organs of 




Fig. 235.— A male mosquito, showing 
auditory hairs (a. h.) on the an- 
tennae. 



THE SPECIAL SENSES 383 

many sound-making insects are known ; but certain other 
insects, that make no sound that we can hear, neverthe- 
less possess similar sound-making organs. 

Sound is produced by mammals and birds by the strik- 
ing of the air which goes to and comes from the lungs 
against certain vibratory cords or flaps in the air-tubes. 
Sounds made by this vibration are re-enforced and made 
louder by arrangements of the air-tubes and mouth for 
resonance, and the character or quality of the sound is 
modified at will to a greater or less degree by the lips and 
teeth and other mouth structures. Sounds so made are 
said to be produced by a voice, or animals making sounds 
in this way are said to possess a voice. Animals possessing 
a voice have far more range and variety in their sound- 
making than most of the animals which produce sounds in 
other ways. The marvelous variety and the great strength 
of the singing of birds and of the cries and roars of mam- 
mals are unequaled by the sounds of any other animals. 

But many animals without a voice — that is, which do not 
make sounds from the air-tubes — make sounds, and some 
of them, as certain insects, show much variety and range 
in their singing. The sounds of insects are made by the 
rapid vibrations of the wings, as the humming or buzzing 
of bees and flies, by the passage of air out or into the body 
through the many breathing pores or spiracles (a kind 
of voice), by the vibration of a stretched membrane or 
tympanum, as the loud shrilling of the cicada, and most 
commonly by stridulation — that is, by rubbing together 
two roughened parts of the body. The male crickets and 
the male katydids rub together the bases of their wing 
covers to produce their shrill singing. The locusts or 
grasshoppers make sounds when at rest by rubbing the 
roughened inside of their great leaping legs against the 
upper surface of their wing covers, and when in flight by 
striking the two wings of each side together* Numerous 
other insects make sounds by stridulation, but many of 



384 ANIMAL STUDIES 

these sounds are so feeble or so high in pitch that they are 
rarely heard by us. Certain butterflies make an odd click- 
ing sound, as do some of the water-beetles. In Japan, 
where small things which are beautiful are prized not less 
than large ones, singing insects are kept in cages and 
highly valued, so that their capture becomes a lucrative 
industry, just as it is with song birds in Europe and Amer- 
ica. Among the many species of Japanese singing insects 
is a night cricket, known as the bridle-bit insect, because 
its note resembles the jingling of a bridle-bit. 

297. The sense of sight. — !Sot all animals have eyes. 
The moles which live underground, insects, and other ani- 
mals that live in caves, and the deep-sea fishes which live 
in waters so deep that the light of the sun never comes 
to them, have no eyes at all, or have eyes of so rudimentary 
a character that they can no longer be used for seeing. 
But all these eyeless animals have no eyes because they 
live under conditions where eyes are useless. They have 
lost their eyes by degeneration. There are, however, many 
animals that have no eyes, nor have they or their ancestors 
ever had eyes. These are the simplest, most lowly organ- 
ized animals. Many, perhaps all eyeless animals are, how- 
ever, capable of distinguishing light from darkness. They 
are sensitive to light. An investigator placed several indi- 
viduals of the common, tiny fresh-water polyp {Hydra) in a 
glass cylinder the walls of which were painted black. He 
left a small part of the cylinder unpainted, and in this part 
of the cylinder where the light penetrated the Hydras all 
gathered. The eyeless maggots or larvae of flies, when 
placed in the light will wriggle and squirm away into dark 
crevices. They are conscious of light when exposed to it, 
and endeavor to shun it. Most plants turn their leaves 
toward the light ; the sunflowers turn on their stems to 
face the sun. Light seems to stimulate organisms whether 
they have eyes or not, and the organisms either try to get 
into the light or to avoid it. But this is not seeing. 



THE SPECIAL SENSES 



385 



The simplest eyes, if we may call them eyes, are not 
capable of forming an image or picture of external objects. 
They only make the animal better capable of distinguish- 
.ing between light and darkness or shadow. Many lowly 
organized animals, as some polyps, and worms, have certain 
cells of the skin specially provided with pigment. These 
cells grouped together form what is called a pigment fleck, 
which can, because of the presence of the pigment, absorb 
more light than the skin cells, and are more sensitive to 
the light. By such pigment-flecks, or eye-spots, the animal 
can detect, by their shadows, the passing near them of mov- 
ing bodies, and thus be in some measure informed of the 
approach of enemies or of prey. Some of these eye-flecks 
are provided, not simply with pigment, but with a simple 
sort of lens that serves to concentrate rays of light and 

make this simplest 
sort of eye even 
more sensitive to 
changes in the in- 
tensity of light 
(Fig. 236). 

Most of the 
many - celled ani- 
mals possess eyes 
by means of which 
a picture of exter- 
nal objects more or less nearly complete and perfect can 
be formed. There is great variety in the finer structure 
of these picture-forming eyes, but each consists essentially 
of an inner delicate or sensitive nervous surface called the 
retina, which is stimulated by light, and is connected with 
the brain by a large optic nerve, and of a transparent light- 
refracting lens lying outside of the retina and exposed to 
the light. These are the constant essential parts of an 
image - forming and image -perceiving eye. In most eyes 
there are other accessory parts which may make the whole 




Fig. 236.— The simple eye of a jelly-fish (Lizzia 
koellikeri).— After O. and K. Hertwig. 



386 



ANIMAL STUDIES 



eye an organ of excessively complicated structure and of 
remarkably perfect seeing capacity. Our own eyes are 
organs of extreme structural complexity and of high de- 
velopment, although some of the other vertebrates have 
undoubtedly a keener and more nearly perfected sight. 

The crustaceans and insects have eyes of a peculiar 
character called compound eyes. In addition most insects 
have smaller simple eyes. Each of the compound eyes is 
composed of many (from a few, as in certain ants, to as 
many as twenty-five thousand, as in certain beetles) eye ele- 
ments, each eye element seeing independently of the other 
eye elements and seeing only a very small part of any ob- 
ject in front of the whole eye. All these small parts of 
the external object seen by the many distinct eye elements 
are combined so as to form an image in mosaic — that is, 
made up of separate small parts — of the external object. 
If the head of a dragon-fly be exam- 
ined, it will be seen that 
two thirds or more of the 



Y 





-A dragon-fly. showing the large com- 
pound eyes on the head. 



Fig. 238.— Some of the facets 
of the compound eye of a 
dragon-fly. 



whole head is made up of the two large compound eyes 
(Fig. 237), and with a lens it may be seen that the outer 
surface of each of these eyes is composed of many small 
spaces or facets (Fig. 238) which are the outer lenses of 
the many eye elements composing the whole eye. 



CHAPTER XXVI 

INSTINCT AND REASON 

298. Irritability. — All animals of whatever degree of 
organization show in life the quality of irritability or re- 
sponse to external stimulus. Contact with external things 
produces some effect on each of them, and this effect is 
something more than the mere mechanical effect on the 
matter of which the animal is composed. In the one- 
celled animals the functions of response to external stimu- 
lus are not localized. They are the property of any part of 
the protoplasm of the body. Just as breathing or digestion 
is a function of the whole cell, so are sensation and response 
in action. In the higher or many-celled animals each of 
these functions is specialized and localized. A certain set 
of cells is set apart for each function, and each organ or 
series of cells is released from all functions save its own. 

299. Nerve cells and fibers. — In the development of the 
individual animal certain cells from the primitive external 
layer or ectoblast of the embryo are set apart to preside 
over the relations of the creature to its environment. 
These cells are highly specialized, and while some of them 
are highly sensitive, others are adapted for carrying or 
transmitting the stimuli received by the sensitive cells, and 
still others have the function of receiving sense-impressions 
and of translating them into impulses of motion. The 
nerve cells are receivers of impressions. These are gathered 
together in nerve masses or ganglia, the largest of these . 
being known as the brain, the ganglia in general being 
known as nerve centers. The nerves are of two classes. 

387 



388 ANIMAL STUDIES 

The one class, called sensory nerves, extends from the skin 
or other organ of sensation to the nerve center. The nerves 
of the other class, motor nerves, carry impulses to motion. 

300. The brain or sensorium. — The brain or other nerve 
center sits in darkness surrounded by a bony protecting 
box. To this main nerve center, or sensorium, come the 
nerves from all parts of the body that have sensation, 
the external skin as well as the special organs of sight, 
hearing, taste, smell. With these come nerves bearing sen- 
sations of pain, temperature, muscular effort — all kinds of 
sensation which the brain can receive. These nerves are 
the sole sources of knowledge to any animal organism. 
Whatever idea its brain may contain must be built up 
through these nerve impressions. The aggregate of these 
impressions constitute the world as the organism knows it. 
All sensation is related to action. If an organism is not 
to act, it can not feel, and the intensity of its feeling is 
related to its power to act. 

301. Reflex action. — These impressions brought to the 
brain by the sensory nerves represent in some degree the 
facts in the animal's environment. They teach something 
as to its food or its safety. The power of locomotion is 
characteristic of animals. If they move, their actions must 
depend on the indications carried to the nerve center from 
the outside; if they feed on living organisms, they must 
seek their food ; if, as in many cases, other living organ- 
isms prey on them, they must bestir themselves to escape. 
The impulse of hunger on the one hand and of fear on the 
other are elemental. The sensorium receives an impression 
that food exists in a certain direction. At once an impulse 
to motion is sent out from it to the muscles necessary to 
move the body in that direction. In the higher animals 
these movements are more rapid and more exact. This is 
because organs of sense, muscles, nerve fibers, and nerve 
cells are all alike highly specialized. In the star-fish the 
sensation is slow, the muscular response sluggish, but the 



INSTINCT AND REASON 389 

method remains the same. This is simple reflex action, an 
impulse from the environment carried to the brain and 
then unconsciously reflected back as motion. The impulse 
of fear is of the same nature. Strike at a dog with a whip, 
and he will instinctively shrink away, perhaps with a cry. 
Perhaps he will leap at you, and you unconsciously will try 
to escape from him. Keflex action is in general uncon- 
scious, but with animals as with man it shades by degrees 
into conscious action, and into volition or action " done on 
purpose." 

302. Instinct. — Different one-celled animals show differ- 
ences in method or degree of response to external influences. 
The feelers of the Amoeba will avoid contact with the feel- 
ers or pseudopodia of another Amoeba, while it does not 
shrink from contact with itself or with an organism of un- 
like kind on which it may feed. Most Protozoa will discard 
grains of sand, crystals of acid, or other indigestible object. 
Such peculiarities of different forms of life constitute the 
basis of instinct. 

Instinct is automatic obedience to the demands of ex- 
ternal conditions. As these conditions vary with each kind 
of animal, so must the demands vary, and from this arises 
the great variety actually seen in the instincts of different 
animals. As the demands of life become complex, so may 
the instincts become so. The greater the stress of envi- 
ronment, the more perfect the automatism, for impulses to 
safe action are necessarily adequate to the duty they have 
to perform. If the instinct were inadequate, the species 
would have become extinct. The fact that its individuals 
persist shows that they are provided with the instincts 
necessary to that end. Instinct differs from other allied 
forms of response to external condition in being hereditary, 
continuous from generation to generation. This suffi- 
ciently distinguishes it from reason, but the line between 
instinct and reason and other forms of reflex action can 
not be sharply drawn. 



390 ANIMAL STUDIES 

It is not necessary to consider here the question of the 
origin of instincts. Some writers regard them as " inherited 
habits," while others, with apparent justice, doubt if mere 
habits or voluntary actions repeated till they become a 
" second nature " ever leave a trace upon heredity. Such 
investigators regard instinct as the natural survival of those 
methods of automatic response which were most useful to 
the life of the animal, the individuals having less effective 
methods of reflex action having perished, leaving no pos- 
terity. 

An example in point would be the homing instinct of 
the fur-seal. When the arctic winter descends on its home 
in the Pribilof Islands in Bering Sea, these animals take 
to the open ocean, many of them swimming southward as 
far as the Santa Barbara Islands in California, more than 
three thousand miles from home. While on the long swim 
they never go on shore, but in the spring they return to 
the northward, finding the little islands hidden in the arc- 
tic fogs, often landing on the very spot from which they 
were driven by the ice six months before, and their arrival 
timed from year to year almost to the same day. The per- 
fection of this homing instinct is vital to their life. If 
defective in any individual, he would be lost to the herd 
and would leave no descendants. Those who return be- 
come the parents of the herd. As to the others the rough 
sea tells no tales. We know that, of those that set forth, a 
large percentage never comes back. To those that return 
the homing instinct has proved adequate. This must be so 
so long as the race exists. The failure of instinct would 
mean the extinction of the species. 

303. Classification of instincts. — The instincts of animals 
may be roughly classified as to their relation to the indi- 
vidual into egoistic and altruistic instincts. 

Egoistic instincts are those which concern chiefly the 
individual animal itself. To this class belong the instincts 
of feeding, those of self-defense and of strife, the instincts 



INSTINCT AND REASON 391 

of play, the climatic instincts, and environmental instincts, 
those which direct the animal's mode of life. 

Altruistic instincts are those which relate to parent- 
hood and those which are concerned with the mass of indi- 
viduals of the same species. The latter may he called the 
social instincts. In the former class, the instincts of par- 
enthood, may be included the instincts of courtship, re- 
production, home-making, nest-building, and care for the 
young. 

304. Feeding. — The instincts of feeding are primitively 
simple, growing complex through complex conditions. 
The protozoan absorbs smaller creatures which contain 
nutriment. The sea-anemone closes its tentacles over its 
prey. The barnacle waves its feelers to bring edible crea- 
tures within its mouth. The fish seizes its prey by direct 
motion. The higher vertebrates in general do the same, 
but the conditions of life modify this simple action to a 
very great degree. 

In general, animals decide by reflex actions what is 
suitable food, and by the same processes they reject poisons 
or unsuitable substances. The dog rejects an apple, while 
the horse rejects a piece of meat. Either will turn away 
from an offered stone. Almost all animals reject poisons 
instantly. Those who fail in this regard in a state of 
nature die and leave no descendants. The wild vetches or 
" loco-weeds " of the arid regions affect the nerve centers of 
animals and cause dizziness or death. The native ponies 
reject these instinctively. This may be because all ponies 
which have not this reflex dislike have been destroyed. 
The imported horse has no such instinct and is poisoned, 
Yery few animals will eat any poisonous object with which 
their instincts are familiar, unless it be concealed from smell 
and taste. 

In some cases, very elaborate instincts arise in connec- 
tion with feeding habits. With the California woodpeckers 
{Melanerpes formicivorus hairdii) a large number of them 



B92 ANIMAL STUDIES 

together select a live-oak tree for their operations. They 
first bore its bark full of holes, each large enough to hold 
an acorn. Then into each hole an acorn is thrust (Figs. 
162 and 163). Only one tree in several square miles may be 
selected, and when their work is finished all those inter- 
ested go about their business elsewhere. At irregular in- 
tervals a Jozen or so come back with much clamorous dis- 
cussion to look at the tree. When the right time comes, 
they all return, open the acorns one by one, devouring 
apparently the substance of the nut, and probably also the 
grubs of beetles which have developed within. When the 
nuts are ripe, again they return to the same tree and the 
same process is repeated. In the tree figured this has been 
noticed each year since 1891. 

305. Self-defense. — The instinct of self-defense is even 
more varied in its manifestations. It may show itself 
either in the impulse to make war on an intruder or in the 
desire to flee from its enemies. Among the flesh-eating 
mammals and birds fierceness of demeanor serves both for 
the securing of food and for protection against enemies. 
The stealthy movements of the lion, the skulking habits of 
the wolf, the sly selfishness of the fox, the blundering good- 
natured power of the bear, the greediness of the hyena, are 
all proverbial, and similar traits in the eagle, owl, hawk, 
and vulture are scarcely less matters of common observa- 
tion. 

Herbivorous animals, as a rule, make little direct resist- 
ance to their enemies, depending rather on swiftness of 
foot, or in some cases on simple insignificance. To the lat- 
ter cause the abundance of mice and mouse-like rodents 
may be attributed, for all are the prey of carnivorous beasts 
and birds, and even snakes. 

Even young animals of any species show great fear of 
their hereditary enemies. The nestlings in a nest of the 
American bittern when one week old showed no fear of 
man, but when two weeks old this fear was very manifest 



INSTINCT AND REASON 



393 



(Figs. 239 and 240). Young mocking-birds will go into 
spasms at the sight of an owl or a cat, while they pay little 
attention to a dog or a hen. Monkeys that have never 
seen a snake show almost hysterical fear at first sight of 
one, and the same kind of feeling is common to most 
men. A monkey was allowed to open a paper bag which 




Fig. 239.— Nestlings of the American bittern. Two of a brood of four birds one week 
old, at whicli age they showed no fear of man. Photograph by E. H. Tabor, 
Meridian, N. Y., May 31, 1898. (Permission of Macmillan Company, publishers of 
Bird-Lore.) 



contained a live snake. He was staggered by the aight, 
but after a while went back and looked in again, to repeat 
the experience. Each wild animal has its special instinct 
of resistance or method of keeping off its enemies. The 
stamping of a sheep, the kicking of a horse, the running 
in a circle of a hare, and the skulking in a circle of some 
foxes, are examples of this sort of instinct. 
2fi 



394 



ANIMAL STUDIES 



306, Play. — The play instinct is developed in numerous 
animals. To this class belong the wrestlings and mimic 
fights of young dogs, bear cubs, seal pups, and young 
beasts generally. Cats and kittens play with mice. Squir- 




of man. Photograph by F. M. Chapman. Meridian. N. Y., June 8, 1898. (Per- 
mission of Macmillan Company, publishers of Bird-Lore.) 

rels play in the trees. Perhaps it is the play impulse which 
leads the shrike or butcher-bird to impale small birds and 
beetles on the thorns about its nest, a ghastly kind of orna- 
ment that seems to confer satisfaction on the bird itself. 
The talking of parrots and their imitations of the sounds 
they hear seem to be of the nature of play. The greater 



INSTINCT AND REASON 395 

their superfluous energy the more they will talk. Much of 
the singing of birds, and the crying, calling, and howling of 
other animals, are mere play, although singing primarily be- 
longs to the period of reproduction, and other calls and 
cries result from social instincts or from the instinct to 
care for the young. 

307. Climate. — Climatic instincts are those which arise 
from the change of seasons. When the winter comes the 
fur-seal takes its long swim to the southward; the wild 
geese range themselves in wedge-shaped flocks and fly high 
and far, calling loudly as they go ; the bobolinks straggle 
away one at a time, flying mostly in the night, and most of 
the smaller birds in cold countries move away toward the 
tropics. All these movements spring from the migratory 
instinct. Another climatic instinct leads the bear to hide 
in a cave or hollow tree, where he sleeps or hibernates till 
spring. In some cases the climatic instinct merges in the 
homing instinct and the instinct of reproduction. When 
the birds move north in the spring they sing, mate, and 
build their nests. The fur-seal goes home to rear its young. 
The bear exchanges its bed for its lair, and its first business 
after waking is to make ready to rear its young. 

308. Environment. — Environmental instincts concern 
the creature's mode of life. Such are the burrowing instincts 
of certain rodents, the woodchucks, gophers, and the like. 
To enumerate the chief phases of such instincts would be 
difficult, for as all animals are related to their environ- 
ment, this relation must show itself in characteristic in- 
stincts. 

309. Courtship.— The instincts of courtship relate chiefly 
to the male, the female being more or less passive. Among 
many fishes the male struts before the female, spreading 
his fins, intensifying his pigmented colors through muscu- 
lar tension, and in such fashion as he can makes himself the 
preferred of the female. In the little brooks in spring 
male minnows can be found with warts on the nose or head, 



396 ANIMAL STUDIES 

with crimson pigment on the fins, or blue pigment on the 
back, or jet-black pigment all over the head, or with varied 
combinations of all these. Their instinct is to display all 
these to the best advantage, even though the conspicuous 
hues lead to their own destruction. Against this contin- 
gency Nature provides a superfluity of males. 

Among the birds the male in spring is in very many 
species provided with an ornamental plumage which he 
sheds when the breeding season is over. The scarlet, crim- 
son, orange, blue, black, and lustrous colors of birds are 
commonly seen only on the males in the breeding season, 
the young males and all males in the fall having the plain 
brown gray or streaky colors of the female. Among the 
singing birds it is chiefly the male that sings, and his voice 
and the instinct to use it are commonly lost when the young 
are hatched in the nest. 

Among polygamous mammals the male is usually much 
larger than the female, and his courtship is often a 
struggle with other males for the possession of the female. 
Among the deer the male, armed with great horns, fight 
to the death for the possession of the female or for the 
mastery of the herd. The fur-seal has on an average a 
family of about thirty-two females, and for the control of 
his harem others are ready at all times to dispute the pos- 
session. But with monogamous animals like the true or 
hair seal or the fox, where a male mates with a single 
female, there is no such discrepancy in size and strength, 
and the warlike force of the male is spent on outside ene- 
mies, not on his own species. 

310. Reproduction. — The movements of many migra- 
tory animals are mainly controlled by the impulse to repro- 
duce. Some pelagic fishes, especially flying-fishes and fishes 
allied to the mackerel, swim long distances to a region 
favorable for a deposition of spawn. Some species are 
known only in the waters they make their breeding homes, 
th^> «vdividuals being scattered through the wide seas at 



INSTINCT AND REASON 397 

other times. Many fresh-water fishes, as trout, suckers, 
etc., forsake the large streams in the spring, ascending the 
small brooks where they can rear their young in greater 
safety. Still others, known as anadromous fishes, feed 
and mature in the sea, but ascend the rivers as the im- 
pulse of reproduction grows strong. Among such species 
are the salmon, shad, alewife, sturgeon, and striped bass in 
American waters. The most noteworthy case of the ana- 
dromous instinct is found in the king salmon or quinnat 
of the Pacific coast. This great fish spawns in ^November. 
In the Columbia River it begins running in March and 
April, spending the whole summer in the ascent of the 
river without feeding. By autumn the individuals are 
greatly changed in appearance, discolored, worn, and distort- 
ed. On reaching the spawning beds, some of them a thou- 
sand miles from the sea, the female deposits her eggs in 
the gravel of some shallow brook. After they are fertilized 
both male and female drift tail foremost and helpless down 
the stream, none of them ever surviving to reach the sea. 
The same habits are found in other species of salmon of 
the Pacific, but in most cases the individuals of other spe- 
cies do not start so early or run so far. A few species of 
fishes, as the eel, reverse this order, feeding in the rivers 
and brackish creeks, dropping down to the sea to spawn. 

The migration of birds has relation to reproduction as 
well as to changes of weather. As soon as they reach their 
summer homes, courtship, mating, nest-building, and the 
care of the young occupy the attention of every species. 

311. Care of the young. — In the animal kingdom one of 
the great factors in development has been the care of the 
young. This feature is a prominent one in the specializa- 
tion of birds and mammals. When the young are cared for 
the percentage of loss in the struggle for life is greatly re- 
duced, the number of births necessary to the maintenance 
of the species is much less, and the opportunities for spe- 
cialization in other relations of life are much greater. 



398 ANIMAL STUDIES 

In these regards, the nest-building and home-making 
animals have the advantage over those that have not these 
instincts. The animals that mate for life have the advan- 
tage over polygamous animals, and those whose social or 
mating habits give rise to a division of labor over those 
with instincts less highly specialized. 

The interesting instincts and habits connected with nest 
or home building and the care of the young are discussed 
in the next chapter. 

312. Variability of instincts. — When we study instincts 
of animals with care and in detail, we find that their regu- 
larity is much less than has been supposed. There is as 
much variation in regard to instinct among individuals as 
there is with regard to other characters of the species. 
Some power of choice is found in almost every operation of 
instinct. Even the most machine-like instinct shows some 
degree of adaptability to new conditions. On the other 
hand, in no animal does reason show entire freedom from 
automatism or reflex action. " The fundamental identity 
of instinct with intelligence," says an able investigator, " is 
shown in their dependence upon the same structural mech- 
anism (the brain and nerves) and in their responsive adap- 
tability." 

313. Reason. — Eeason or intellect, as distinguished from 
instinct, is the choice, more or less conscious, among re- 
sponses to external impressions. Its basis, like that of in- 
stinct, is in reflex action. Its operations, often repeated, 
become similarly reflex by repetition, and are known as 
habit. A habit is a voluntary action repeated until it be- 
comes reflex. It is essentially like instinct in all its mani- 
festations. The only evident difference is in its origin. 
Instinct is inherited. Habit is the reaction produced with- 
in the individual by its own repeated actions. In the 
varied relations of life the pure reflex action becomes inade- 
quate. The sensorium is offered a choice of responses. To 
choose one and to reject the others is the function of intel- 



INSTINCT AND REASON 399 

lect or reason. While its excessive development in man 
obscures its close relation to instinct, both shade off by 
degrees into reflex action. Indeed, no sharp line can be 
drawn between unconscious and subconscious choice of 
reaction and ordinary intellectual processes. 

Most animals have little self-consciousness, and their 
reasoning powers at best are of a low order ; but in kind, 
at least, the powers are not different from reason in man. 
A horse reaches over the fence to be company to another. 
This is instinct. When it lets down the bars with its teeth, 
that is reason. When a dog finds its way home at night by 
the sense of smell, this may be instinct ; when he drags a 
stranger to his wounded master, that is reason. When a 
jack-rabbit leaps over the brush to escape a dog, or runs in 
a circle before a coyote, or when it lies flat in the grass as a 
round ball of gray indistinguishable from grass, this is in- 
stinct. But the same animal is capable of reason — that is, 
of a distinct choice among lines of action. Not long ago a 
rabbit came bounding across the university campus at Palo 
Alto. As it passed a corner it suddenly faced two hunting 
dogs running side by side toward it. It had the choice of 
turning back, its first instinct, but a dangerous one ; of 
leaping over the dogs, or of lying flat on the ground. It 
chose none of these, and its choice was instantaneous. It 
ceased leaping, ran low, and went between the dogs just as 
they were in the act of seizing it, and the surprise of the 
dogs, as they stopped and tried to hurry around,- was the 
same feeling that a man would have in like circumstances. 

On the open plains of Merced County, California, the 
jack-rabbit is the prey of the bald eagle. Not long since a 
rabbit pursued by an eagle was seen to run among the 
cattle. Leaping from cow to cow, he used these animals 
as a shelter from the savage bird. When the pursuit was 
closer, the rabbit broke cover for a barbed wire fence. 
When the eagle swooped down on it, the rabbit moved a 
few inches to the right, and the eagle could not reach him 



400 ANIMAL STUDIES 

through the fence. When the eagle came down on the 
other side, he moved across to the first. And this was con- 
tinued until the eagle gave up the chase. It is instinct 
that leads the eagle to swoop on the rabbit. It is instinct 
again for the rabbit to run away. But to run along the line 
of a barbed wire fence demands some degree of reason. If 
the need to repeat it arose often in the lifetime of a single 
rabbit it would become a habit. 

The difference between intellect and instinct in lower 
animals may be illustrated by the conduct of certain mon- 
keys brought into relation with new experiences. At one 
time we had two adult monkeys, " Bob " and " Jocko," be- 
longing to the genus Macacus. Xeither of these possessed 
the egg-eating instinct. At the same time we had a baby 
monkey, " Mono," of the genus Cercopithecus. Mono had 
never seen an egg, but his inherited impulses bore a direct 
relation to feeding on eggs, just as the heredity of Macacus 
taught the others how to crack nuts or to peel fruit. 

To each of these monkeys we gave an egg, the first that 
any of them had ever seen. The baby monkey, Mono, 
being of an egg-eating race, devoured his egg by the opera- 
tion of instinct or inherited habit. On being given the 
egg for the first time, he cracked it against his upper teeth, 
making a hole in it, and sucked out all the substance. 
Then holding the egg-shell up to the light and seeing that 
there was no longer anything in it, he threw it away. All 
this he did mechanically, automatically, and it was just as 
well done with the first egg he ever saw as with any other 
he ate. All eggs since offered him he has treated in the 
same way. 

The monkey Bob took the egg for some kind of nut. 
He broke it against his upper teeth and tried to pull off 
the shell, when the inside ran out and fell on the ground. 
He looked at it for a moment in bewilderment, took both 
hands and scooped up the yolk and the sand with which it 
was mixed and swallowed the whole. Then he stuffed the 



INSTINCT AND REASON 401 

shell itself into his mouth. This act was not instinctive. 
It was the work of pure reason. Evidently his race was 
not familiar with the use of eggs and had acquired no in- 
stincts regarding them. He would do it better next time. 
Eeason is an inefficient agent at first, a weak tool; but. 
when it is trained it becomes an agent more valuable and 
more powerful than any instinct. 

The monkey Jocko tried to eat the egg offered him in 
much the same way that Bob did, but, not liking the taste, 
he threw it away. 

The confusion of highly perfected instinct with intellect 
is very common in popular discussions. Instinct grows 
weak and less accurate in its automatic obedience as the 
intellect becomes available in its place. Both intellect and 
instinct are outgrowths from the simple reflex response to 
external conditions. But instinct insures a single definite 
response to the corresponding stimulus. The intellect has 
a choice of responses. In its lower stages it is vacillating 
and ineffective ; but as its development goes on it becomes 
alert and adequate to the varied conditions of life. It 
grows with the need for improvement. It will therefore 
become impossible for the complexity of life to outgrow 
the adequacy of man to adapt himself to its conditions. 

Many animals currently believed to be of high intelli- 
gence are not so. The fur-seal, for example, finds it way 
back from the long swim of two or three thousand miles 
through a foggy and stormy sea, and is never too late or too 
early in arrival. The female fur-seal goes two hundred 
miles to her feeding grounds in summer, leaving the pup 
on the shore. After a week or two she returns to find him 
within a few rods of the rocks where she had left him. 
Both mother and young know each other by call and by 
odor, and neither is ever mistaken, though ten thousand 
other pups and other mothers occupy the same rookery. 
But this is not intelligence. It is simply instinct, because 
it has no element of choice in it. Whatever its ancestors 



402 ANIMAL STUDIES 

were forced to do the fur-seal does to perfection. Its in- 
stincts are perfect as clockwork, and the necessities of 
migration must keep them so. But if brought into new 
conditions it is dazed and stupid. It can not choose when 
different lines of action are presented. 

The Bering Sea Commission once made an experiment 
on the possibility of separating the young male fur-seals, 
or " killables," from the old ones in the same band. The 
method was to drive them through a wooden chute or run- 
way with two valve-like doors at the end. These animals can 
be driven like sheep, but to sort them in the way proposed 
proved impossible. The most experienced males would 
beat + heir noses against a closed door, if they had seen a 
seal before them pass through it. That this door had been 
shut and another opened beside it passed their comprehen- 
sion. They could not choose the new direction. In like 
manner a male fur-seal will watch the killing and skinning 
of his mates with perfect composure. He will sniff at their 
blood with languid curiosity ; so long as it is not his own 
it does not matter. That his own blood may flow out on 
the ground in a minute or two he can not foresee. 

Eeason arises from the necessity for a choice among ac- 
tions. It may arise as a clash among instincts which forces 
on the animal the necessity of choosing. A doe, for ex- 
ample, in a rich pasture has the instinct to feed. It hears 
the hounds and has the instinct to flee. Its fawn may be 
with her and it is her instinct to remain and protect it. 
This may be done in one of several ways. In proportion as 
the mother chooses wisely will be the fawn's chance of sur- 
vival. Thus under difficult conditions, reason or choice 
among actions rises to the aid of the lower animals as well 
as man. 

314. Mind. — The word mind is popularly used in two 
different senses. In the biological sense the mind is the 
collective name for the functions of the sensorium in men 
and animals. It is the sum total of all psychic changes, 



INSTINCT AND REASON 



403 



actions and reactions. Under the head of psychic functions 
are included all operations of the nervous system as well as 
all functions of like nature which may exist in organisms 
without specialized nerve fibers or nerve cells. As thus de- 
fined mind would include all phenomena of irritability, and 
even plants have the rudiments of it. The operations of 
the mind in this sense need not be conscious. With the 
lower animals almost all of them are automatic and uncon- 
scious. With man most of them must be so. All func- 
tions of the sensorium, irritability, reflex action, instinct, 
reason, volition, are alike in essential nature though differ- 
ing greatly in their degree of specialization. 

In another sense the term mind is applied only to con- 
scious reasoning or conscious volition. In this sense it is 
mainly an attribute of man, the lower animals showing it 
in but slight degree. The discussion as to whether lower 
animals have minds turns on the definition of mind, and 
our answer to it depends on the definition we adopt. 




A "pointer" dog in the act of "pointing," a specialized instinct. 
(Permission of G. O. Shields, publisher of Recreation.) 



CHAPTER XXVII 

ECONOMIC ZOOLOGY 

315. Uses of animals to man. — Economic zoology treats 
of the value of animals for the purposes of man. These 
services are enormously varied, and in this chapter we can 
give only a bare enumeration of some of the most conspicu- 
ous lines of service, leaving the student to develop the 
details. At the outset we may remember that most of the 
species of animals have inhabited the earth longer than man 
has, and that we have no right to suppose that the reason 
for their creation was to render him some service. Thou- 
sands and thousands of species can be of no possible use in 
human affairs, and a few are related to man only through 
their ability to inflict positive injury. Of harmful nature 
are the insects with poison glands connected with the 
mouth, many of those with stings, the snakes with venom 
fangs, the poisonous Gila monster among lizards, some of 
the great beasts of prey, and, perhaps most of all, the nox- 
ious types of mosquitoes, who transfer to the human body 
the germs of certain diseases, as malaria, yellow fever, and 
filariasis. Other noxious animals are the vermin — rats and 
mice and the like— which infest houses and may carry dis- 
ease, the many forms of internal and external parasites, 
intestinal worms, ticks, mites, and the like. Harmful in 
other ways are the hordes of insects injurious to vegetation ; 
and some mammals, as rabbits and gophers, are at times 
extremely destructive to valuable plants. 

316. Domestic animals. — The very earliest records of 
man show that he trained those animals about him which 

404 



ECONOMIC ZOOLOGY 405 

could be made to minister to his needs or his pleasure. 
The young of almost any species can be rendered friendly 
and fearless by kind treatment. Naturally those most 
easily tamed and most useful when reared received the 
most attention. Of the young born in domestication, 
those most tractable or most helpful would be most cher- 
ished. Thus during the lapse of ages by a process of selec- 
tion, conscious or unconscious, distinct breeds were formed, 
many of these differing from the original stock more than 
distinct species differ from each other. Varying needs 
brought greater and greater differences among breeds ; thus 
all dogs are domesticated wolves of different species, but 
the distinctions between St. Bernard dogs, Eskimo dogs, 
greyhounds, pugs, lap-dogs, and the tiny hairless Pelon 
dogs of Mexico are far greater than the differences sepa- 
rating different kinds of wolves. 

317. Formation of new races. — With the advance of civili- 
zation unconscious selection has developed into conscious 
choice, and new and improved races can be planned and 
developed with almost absolute certainty of success. Se- 
lective breeding has been called "the magician's wand," 
by which the breeder can summon up new forms useful to 
man or pleasing to his fancy. In general, new varieties are 
formed by crossing old ones, each of which has certain 
desirable traits. These may be combined in certain of the 
young, or other qualities, new or unforeseen, may appear. 
These are retained as the basis of the improved race, while 
those individuals not possessing the desired characters 
are discarded. By pursuing this method for a certain 
number of generations the new type may become more or 
less perfectly established. In this regard almost any desired 
result is possible with time and patience. Those species 
most widely domesticated have, in general, developed the 
greatest number of distinct races or breeds. Among these 
are the dcg, the horse, the donkey, the ox, the sheep, the 
goat, the hog (descended from the wild boar), the rabbit, 



4:06 ANIMAL STUDIES 

the cat, the fowl, the goose, the duck, the peacock, the 
guinea-hen, the camel, the honey-bees, the silk-worm, 
the elephant, the llama, the reindeer, the falcon, the 
turkey, the ferret, the different parrots, the guinea-pig, 
and other species. Those forms domesticated for special 
purposes or within a narrow range are less likely to form 
varieties. 

318. Artificial propagation. — Many animals are bred 
within regions not formerly occupied by them, although 
being in no sense domesticated. Among these are the vari- 
ous kinds of salmon and trout, the shad, the striped bass, 
the carp, goldfish, and many other fishes, the oyster, the 
Chinese pheasant, the lady-birds. In some cases the eggs 
are taken and hatched under artificial conditions. This is 
especially the case with the salmon and trout. In other 
cases the animals are simply liberated in a new region to 
make their way in competition with other species. 

319. Services of animals. — The chief services rendered 
by animals may be treated under the following heads : 

Food, clothing, ornaments, use in the arts, as destroyers 
of injurious animals, as servants, and as friends. 

320. Animals used as food. — All races of men have fed, 
in part at least, on the flesh of animals, either raw or 
cooked. For this purpose certain species have long been 
domesticated. As a rule, those mammals and birds which 
are wholly carnivorous have been rejected by man as unfit 
for food ; but this rule does not apply to the class of 
fishes. Among the animals whose flesh is especially valued 
may be named the ox, the sheep, the goat tribe, the deer 
tribe, the hog, and, in general, all hoofed animals with four 
toes. Besides these, the various rabbits, squirrels, bears, 
raccoons, opossums, fur seals, the large bats, certain 
monkeys, some whales, and a variety of other mammals 
are largely eaten by men on account of the excellence of 
their flesh. All mammals, excepting the strictly carnivo- 
rous cats and wolves, are considered welcome food by some 



ECONOMIC ZOOLOGY 407 

races of men, and even these have not been wholly re- 
jected. 

The milk of the larger hoofed animals — the cow, sheep, 
goat, buffalo, and even the horse and the ass — has formed 
an important part in human diet. 

All the larger birds which are not strictly carnivorous 
are eaten by man, and the eggs of these and many others, 
domestic birds and wild birds, have formed a large part of 
his diet. In China a certain species of swallow (Collocalia) 
forms a nest in part from a secretion from its own stomach. 
This substance forms an agreeable basis for soup, the so- 
called edible bird's-nest. 

Among the reptiles certain species of turtles have flesh 
of great delicacy — for instance, certain land species, as 
the Maryland diamond-back terrapin, and some of the 
great sea-turtles. Among the amphibians, the chief food 
product is found in the delicate muscles of the legs of 
various species of frogs. 

Of the 12,000 known species of fishes, many are too 
small to be worth taking. These serve as food for larger 
fishes. A few dozen species in the tropics have flesh con- 
taining a bitter alkaloid, which is more or less poisonous. 
The great majority are, however, excellent as food, and up- 
ward of 5,000 species may be fairly called food-fishes. Cer- 
tain fishes yield jelly-like substances from the air-bladder 
or other structures. The eggs of the sturgeon are prepared 
to be eaten as " caviar." Among the fishes most delicious 
as food, the eulachon of the Columbia Eiver perhaps ranks 
first. The ayu, oi samlet, of Japan resembles it. Xext we 
may place the pampano of the G-ulf of Mexico, the Spanish 
mackerel of the same region, the whitefish of the Great 
Lakes, the bluefish and weakfish of New England, and the 
various kinds of trout, grayling, bass, shad, and pickerel. 
The sole, the surmullet, and the turbot rank among the 
first of the fishes of Europe. Of far greater economic 
value than any of these, from their exceeding abundance, 



408 



ANIMAL STUDIES 



are the various kinds of salmon, the cod, herring, mackerel, 
and halibut. 

The gelatinous fin-rays of certain sharks (see Fig. 103) 
make an excellent soup, much valued by the Chinese. 

In most regions the flesh of the fish is cooked before 
eating. In arctic regions it is salted or smoked. In Japan 
and Hawaii fishes are largely eaten raw. 

Insects, such as locusts and the larvae of certain beetles, 
are used as human foods by the lowest races only. The 
honey made from nectar gathered from flowers by the hone^ 




Pig. 241.— The palolo or edible worm of the Atlantic {Eunice fucata Ehlers), Tortu- 
gas, Florida.— After A. G. Mayer. 

bee has, however, been regarded as a delicacy by all races of 
men who dwell in regions inhabited by bees. Various crus- 
taceans, as the lobster, cray-fish, and many crabs, are, how- 
ever, much esteemed. The " beche cle mer " is a holothurian 
used as food in the western Pacific ; and many people eat 
certain species of sea-urchins. "Worms have rarely any 
economic value. The common earthworm is, however, of 
the greatest service in pulverizing soils. Certain sea-worms 
are edible. Most notable of these is a worm of the coral 



ECONOMIC ZOOLOGY 409 

reefs called palolo, found about Samoa and Fiji, and a 
second species in the tropical Atlantic. Twice during the 
year — in October and November — the posterior half of the 
body, bearing the reproductive elements, separates from 
the head end of the animal, and swims to the surface for 
spawning purposes. This phenomenon occurs at definite 
times— at dawn of the day on which the moon is in its last 
quarter, and on the day previous. At this season the water 
fairly boils with countless thousands of these headless 
worms, that are collected by the natives and esteemed a 
great delicacy. 

Among the mollusks many species are excellent as food 
for man. Foremost among these is the oyster. With it 
are many species of clam, scallop, cockle, snail, abalone, 
squid, cuttlefish, and octopus. 

321. Clothing from animals. — The hair of certain mam- 
mals may be used as a fabric for cloth. The most valuable 
in this connection is the wool of sheep. Wild sheep have 
little or no wool, the great yield of this article being a 
product of artificial selection. A coarser wool is produced 
by some goats, as also by some animals related to the Peru- 
vian llama. The hair of the camel is used to make a coarse 
cloth. 

Another textile fabric of great importance is silk, which 
is the fine-spun covering of the larvae and chrysalids of a 
white moth. The furs and skins of many animals formed 
the chief clothing of primitive man, and are still largely 
used in cold regions among fashionable as well as primitive 
people. Among the finest of furs are those of the weasel 
tribe, the otter, mink, ermine, marten, and their relatives. 
Most valuable of all these is the fur of the sea-otter of the 
north Pacific, a single skin being sometimes valued at up- 
ward of $1,000. The female and young of the fur seal 
( Otoes) yield a very soft and beautiful fur after the long 
hairs have been plucked out. Many foxes yield delicate 
and beautiful furs. In general, those animals living in the 
27 



410 ANIMAL STUDIES 

coldest regions are most valued, because their hairs are 
longer and more closely set than in similar animals living 
with less need of protection from the cold. Coarser furs 
are taken from the various bears, wolves, and other carnivo- 
rous animals, from wild goats and other animals of north- 
ern or mountainous regions. The skins of tigers, leopards, 
and other large members of the cat family, with short, 
close-set, glossy fur, often beautifully colored, are also 
highly valued. The long, coarse hair of the buffalo caused 
the " buffalo-robe " to be highly appreciated by our fathers 
before the species was exterminated. The skins of animals 
with indifferent fur, as squirrels and prairie-dogs, are often 
stitched together to form blankets. 

The skins of many animals, as the ox, sheep, goat, hair- 
seal, etc., have been tanned as leather. Leather is used for 
shoes for the feet of men. In more primitive times it 
formed a large part of the clothing of men. In Alaska, the 
stomach and intestines of the sea-lion are used for water- 
proof rain-coats. It forms a light and serviceable garment. 
In Japan, slippers are made from the skin of the long- 
haired native monkey. 

The feathers of many birds are used in pillows. Most 
valuable is the down of the breast of the eider-duck. The 
most common feathers for pillows come from the hen and 
the goose. The downy breasts of young eagles are in 
Alaska stitched together to form mantles. The close-set 
feathers of the grebe, a diving water-bird, form a kind of 
fur when the skin is tanned. In Hawaii royal cloaks of 
great cost have been made, the texture filled and colored 
with the scarlet and golden feathers of native song-birds. 

322. Animals as ornaments. — The most valuable ornament 
derived from any animal is the pearl, the product of a large 
bivalve mollusk, the pearl-oyster in tropical seas. The 
pearl is a fine secretion from the mantle of the animal sur- 
rounding a grain of sand or other source of irritation. In 
the museum of Harvard University there is a small fish in- 



ECONOMIC ZOOLOGY 411 

closed in pearl, it having entered the shell for protection. 
Coarser pearls occur in other species. Occasionally valu- 
able ones are found in the river-mussel ( Unio) of our Amer- 
ican streams. Other mollusks, as the abalone on the Pacific 
coast and the Unio, furnish material for buttons or for in- 
laid work. The large scales of certain fishes (as the tarpon) 
serve a similar purpose. The shells of many small sea-snails 
are used as beads, and shells of mollusks as well as skins of 
birds have been used as money by native aboriginal races. 

The fine furs above enumerated are largely used for 
ornament rather than for use. The plumes of various 
birds, notably the ostrich and the egret, are used for orna- 
ment. Dead birds and parts of birds have been worn as 
ornaments on the hats of unthinking women of even civil- 
ized races. Incalculable injury has been done through this 
fashion by the destruction of insect-eating birds. The sing- 
ing-birds of Japan have been practically exterminated by 
the remorseless demands of the milliner, and those of our 
own country have been greatly reduced in number. Ee- 
cently our statutes have protected our own singing-birds, 
but the remorseless destruction of parrots and egrets in 
Mexico and of terns and other beautiful sea-birds for orna- 
mental purposes still goes on. 

323. Animal products used in the arts. — Chief among the 
animal products used in the arts is leather. This is de- 
rived chiefly from the skins of the ox, sheep, and goat, but . 
that of the horse, hog, deer, and many other animals, native 
and domestic, has a certain value. Waterproof shoes are 
made from the skin of the hair-seal. The skin of the alli- 
gator is often tanned for portmanteaus, and the skin of 
snakes for purses. 

Oil is procured from many animals. The fine oil from 
the liver of the codfish is largely used in medicine, being 
readily assimilated. Coarser oils are produced from other 
fishes, especially from the liver of sharks. Still coarser oils 
are taken in large quantities from the blubber of the right 



412 ANIMAL STUDIES 

whale and other large whales. These whales also yield 
whalebone from structures used in straining out their food 
developed on the roof of the mouth. Finer oils come from 
the sperm-whale, the most valued being a wax-like sub- 
stance, spermaceti, found in the head. Ambergris is an 
abnormal secretion sometimes found about the liver of the 
sperm-whale. It has a very high value, being very fragrant 
and used as a perfume. The old-fashioned perfumery 
musk is a secretion of the musk deer ; civet is produced by 
the Viverra, a weasel-like animal of South America. 

Ivory comes from the tusks of the elephant. The long 
teeth of the walrus are very similar to true ivory. 

The horns and bones of different animals have many 
uses in the arts. The quills of birds have also certain uses. 
The scales of sea-tortoises are used in making combs. 
The coloring-matter, cochineal, much used before the in- 
troduction of anilin dyes, came from the bodies of certain 
scale insects living on cactus, chiefly in Mexico. 

324. Animals as enemies and destroyers of enemies of 
man. — The chief enemies of man are the larger carnivorous 
animals which are personally dangerous to him, to his 
flocks, or to his crops. Among these are the great wildcats 
(lion, tiger, leopard, panther, etc.), the wild dogs (wolf, 
coyote, jackal, etc.), the rodents (rabbits, rats, mice) which 
devour his crops or his stores, and the great multitude of 
insects which destroy his crops. 

Against the great carnivora, the dog, itself a tamed 
wolf, is his best defender. The dog, cat, ferret, and mon- 
goose have been brought into his service as destroyers of 
rodents ; the mongoose, by destroying lizards and birds' 
nests also, doing more harm than good. The hawks, owls, 
and snakes also help him in keeping down the numbers of 
rats and mice. 

Against the hordes of noxious insects man's chief natural 
protection is found in the singing-birds, most of whom feed 
on insects which destroy vegetation. He has also a large 



ECONOMIC ZOOLOGY 413 

number of allies among the insects themselves, the help- 
ful forms who destroy those who are noxious or mis- 
chievous. 

325. Economic entomology. — The enormous number of 
insects which feed on useful plants gives this branch of 
science a great practical importance. Most insects feed on 
plants, and those cultivated by man seem to be especially 
chosen. This is due to the great masses of the same spe- 
cies brought together in cultivation. An apple orchard of 
300 acres in New York gives opportunity for the breeding 
of enemies of the apple. A 3,300-acre vineyard in Cali- 
fornia breeds in numbers the insect enemies of the vine. 
The great orchards and gardens may be compared to 
bounteous feasts, and the insect guests come in families and 
remain until the feast is over. 

Probably half the insect species inhabiting the United 
States (upward of 60,000 in all) are injurious to vegetation. 
There is scarcely a plant, wild or cultivated, that does not 
harbor insect pests, there being on an average six insect 
enemies to each species. In Europe 500 species are said to 
attack the oaks, and 400 species the willows. In America 
250 species feed in one way or another on the apple. 

Of each species the number of individuals is enormous, 
for most of them are excessively prolific. Of aphides or 
plant lice there are 12 generations in a year ; 12,000,000 
aphides have been found on a single cherry-tree. The 
grape- destroying insect phylloxera was first discovered in 
New York in 1854= It was carried to France in 1863, and 
in 1879 the valuable vines on 3,000,000 acres in France had 
been destroyed by its root-attacking larvse. 

326. Orchard pests. — In 1878 the " cottony-cushion scale " 
was brought to California from Australia on an orange-tree. 
In. less than ten years almost every orange-tree in Califor- 
nia was attacked by it, and the industry seemed doomed to 
destruction. The pest was checked by the introduction of 
its natural enemy, an Australian lady-bird beetle, called 



414: ANIMAL STUDIES 

Vedalia, equally prolific and quick to spread from tree to 
tree. 

The so-called San Jose scale, long known in California, 
but probably introduced from Asia, is now the worst pest of 
the orchards of the United States. It is found in 35 States, 
and in most of these statutes exist aiming at its suppression. 

327. Amount of insect destruction. — In 1864 the loss of 
wheat and corn in Illinois caused by the chinch-bug 
amounted to $73,000,000. In 1874 the total loss in the 
United States amounted to $100,000,000. In 1874 the 
Eocky Mountain locust destroyed in the States between 
the Missouri Eiver and the Eocky Mountains crops amount- 
ing to $100,000,000. 

From 18G4 to 1878 the cotton-worm in the Southern 
States destroyed each year $30,000,000 worth of cotton. 
The Hessian fly has often destroyed $50,000,000 worth of 
grain in a single year in the United States. Ten per cent, 
of the field-crops of our country are each year by noxiour 
insects. The annual loss from this source has been calcu 
lated to be $300,000,000. 

328. Prevention of insect ravages. — These ravages can 
not be prevented, but they can be materially checked. A 
few examples of insect fighting may be given : 

The cottony-cushion scale was virtually exterminated by 
the introduction of its enemy at home. This can be done 
with various other species. 

In Indiana the destructive corn-root worm was destroyed 
by rotation of crops, introducing something on which the 
larvae could not feed. 

Many insects are killed by insecticides, washes, and 
sprays, or by fumigation with gas. The Department of 
Agriculture maintains a division devoted to insect fight- 
ing. It costs now about $75,000 a year, and saves the 
farmers and gardeners many times that amount. 

The preservation of insect-eating birds is an effective 
method of insect fighting. 



ECONOMIC ZOOLOGY 415 

329. Beneficial insects. — Many insects are useful from 
their habit of devouring the noxious species. The lady- 
bird beetles feed on scale-insects and plant-lice. The ich- 
neumon flies lay their eggs in the larvae of many species. 
The carrion-beetles and others are valuable as scavengers, 
as are various flies. 

330. Animals as servants. — As servants of man, the horse, 
the donkey, the ox, the goat, the dog, the elephant, the 
camel, the llama, the reindeer, the buffalo of Europe, the 
water-buffalo of the East Indies, have been with him from 
the dawn of history, and the help they render needs no 
description here. 

331. Animals as friends.— In the category of higher 
service to man, the service of friendship, the dog stands 
nearest. The cat always thinks of herself first, but the dog 
will lay down his life for his master, or even for his own 
feeling of duty. The monkey is devoted to his own kind, 
and may be equally devoted to his master, while his 
thoughts and disposition run in closer parallelism. But 
the monkeys for the most part are subject to violent fits of 
passion over which at the best they have little control. 
The anger or jealousy of some of the larger monkeys is often 
dangerous to human life. Eor this reason men have rarely 
admitted monkeys to their circle of personal friends. In 
some respects the gentle, wistful little marmosets of South 
America constitute an exception to the rule of quick temper 
among monkeys. To the circle of personal intimacy the 
dog can often rise, and the horse also so far as he can un- 
derstand. 

Other friends of man are the singing-birds, those who 
can be happy even though caged. Easily first of these is 
the mocking-bird. The bobolink, most joyous of birds, the 
nightingale, sweetest of all singers, the wood-thrush, and 
the skylark can scarcely be reared in cages. Other attractive 
cage-birds are the cardinal grosbeak, the canary-bird, the 
Japanese finch, and the many species of parrot, who use 



416 ANIMAL STUDIES 

their hours of loneliness in human society by picking up 
and repeating the phrases they hear. They show a skill in 
imitation and a capacity of association of ideas unequaled 
by any other of the lower animals. In Japan certain kinds 
of chirping insects, cicadas and the like, are kept in cages 
in homes, affording great delight to their owners. 



CHAPTER XXVIII 

THE ANIMALS OF THE PAST 

332. Extinct animals— The mammoth. —The animals alive 
to-day are but the merest fraction of all that have been. 
Xew species of animals long since vanished from the face 
of the earth are continually being discovered. Notable 
among fossilized remains are those of the mammoth, an 
enormous elephant, specimens of which, not even decayed, 
have been found frozen in the ice of northern Siberia. 
Some of the specimens discovered were complete with skele- 
ton, flesh, and hair. Its like exists no longer. It resembled 
an elephant much more than any other kind of living ani- 
mal, but it was twice the bulk and weight of the largest 




I?ig. 242. — Rough drawing of a mammoth, on its own ivory, by a contemporary man.— 
After Le Contb. 

living elephant and a third taller. Its body was covered 
in places with a brownish wool, in others with long hair. 
Bones and other remains of many mammoths have been 

417 



418 



ANIMAL STUDIES 



found in various parts of America and Europe. It is be- 
lieved that immense herds of this great mammal once 




roamed all over Europe and the northern parts of Xorth 
America. But no living mammoths are known. It is an 
extinct species of elephant. 



THE ANIMALS OF THE PAST 419 

There was once found in France a rude drawing (Fig. 
242) of the mammoth made on ivory cut from its own 
tusks, evidently sketched by a man living in that time. 
This drawing shows that the mammoth was not extinct at 
the time of the earliest man. 

Still another huge extinct animal resembling the ele- 
phant, but with very different teeth, is known as the mas- 
todon. 

333. Extinct birds. — In New Zealand and Madagascar are 
found bones and eggs of huge birds {Dinornis and JEpyor- 
nis) which must have been twelve feet high, and which had 
toe-bones as large as those of an elephant. These birds 
are long since extinct, and they are not even recorded in 
history. In Mauritius there once lived a heavy, clumsy 
bird called the dodo. No living specimens exist, although 
a few live dodos were known not more than one hundred 
and fifty or two hundred years ago. It was unable to fly, 
weighed as much as fifty pounds, and was covered with soft, 
downy feathers like a new-born chicken. This bird has 
become extinct in comparatively recent years. Several 
stuffed specimens are still to be found in museums. 

334. Animals becoming extinct. — In New Zealand there 
may be still living a few individuals of another strange, 
wingless bird called the Apteryx. This bird is disappearing 
in our own times. Similarly in North America the bison, 
or buffalo, which roamed the great Western plains in enor- 
mous herds only a score of years ago, is now represented by 
not more than a few hundred individuals living in a state 
of nature. A few hundred others may be found in zoolog- 
ical gardens and parks. The extinction of the North Amer- 
ican buffalo is taking place in our generation. The great 
auk, a large sea-bird of the Atlantic, has disappeared dur- 
ing the present century. The sea-cow (Hydrodamalis), a 
huge, herbivorous creature, living in the sea and feeding 
on seaweed, was one hundred and fifty years ago abundant 
about the Commander Islands, off Kamchatka. It was used 



420 ANIMAL STUDIES 

as food by sailors, and thus was soon destroyed. It is now 
known only by its bones preserved in a few museums. The 
passenger-pigeon of America, which migrated north and 
south through the Mississippi Valley in flocks of such 
countless numbers that the sun was darkened as it passed, 
and which loaded the forest trees of Kentucky with its 
nests a few decades ago, is now a rare bird, a treasure in 
the museums. 

335. Fossils. — Of all these recently extinct animals, we 
have preserved to us bones, or stuffed specimens, or eggs, 
as well as the records of personal observation. But we 
know of the former existence of thousands and thousands 
of other animals, now extinct, through remains of another 
kind. These are either actual remains of bones or other 
parts preserved intact in soil or rocks, or else, and more 
commonly, parts of the animals which have been turned 
into stone, or of which stony casts have been made. All 
such remains buried by natural causes are called fossils. 
The process by which they are sometimes changed from 
animal substance into stone is called petrifaction. 

Fossils may be of three kinds. In the case of recently 
extinct animals, bones or other parts of the body may be- 
come buried in the soil and lie there for a long time with- 
out any change of organic into inorganic matter. Thus 
fossil insects are found with the bodies preserved intact in 
amber, a fossil resin from some ancient and extinct pine- 
tree. Over 800 species of extinct insects are known from 
amber fossils. The bones of the earliest members of the 
elephant family, the teeth of extinct sharks, and the shells 
of extinct mollusks have also been found intact, still com- 
posed of their original matter. 

In the second kind of fossils the original or organic 
matter is gone, the organic form and organic structure 
being preserved in mineral matter. That is, the organic 
matter has been slowly and exactly replaced by mineral 
matter. As each particle of organic matter passed away by 



THE ANIMALS OF THE PAST 421 

decay, its place was taken by a particle of mineral matter. 
These are called petrifactions. This is beautifully shown 
in the case of petrified wood. We can cut and grind thin 
a bit of petrified wood, and see in it, with the microscope, 
the exact details of its original fine cellular structure. 
This substituted mineral matter may be almost any mineral, 
but usually it is silica (quartz), or carbonate of lime (lime- 
stone), or sulphide of iron (iron pyrites). In the case of 
animal parts which were originally partly organic and 
partly inorganic, as bones and teeth and shells, often the 
organic matter only is replaced by the petrifying mineral, 
although sometimes the old inorganic matter is also thus 
replaced. Finally, sometimes the organic matter and 
organic structure are both lost, only the original outline 
or form of the whole part being retained. This occurs 
when the organic matter imbedded in mud and clay decays 
away, leaving a hollow which is filled up by some mineral 
different from the matrix. In this case the fossil is simply 
a cast of the original organic remains. 

336. Fossil-bearing rocks and their origin. — Examination 
and study of the rocks of the earth reveal the fact that 
fossils, or the remains of animals and plants, are found in 
certain kinds of rocks only. They are not found in lava, 
because lava comes from volcanoes as a red-hot, viscous 
liquid, which cools to form the hard lava. No animal or 
plant caught in a lava stream will leave any trace. Fur- 
thermore, fossils are not found in granite, nor in metals, 
nor in certain other of the common rocks. Many rocks 
are, like lava, of igneous origin ; others, like granite, 
although not originally in melted condition, have been so 
heated subsequent to their formation, that any traces of 
animal or plant remains in them have been obliterated. 
Fossils are found almost exclusively in rocks which have 
been formed by the slow deposition in water of sand, clay, 
mud, or lime. The sediment which is carried into a lake or 
ocean by the streams opening into it sinks slowly to the 



422 ANIMAL STUDIES 

bottom of the lake or ocean and forms there a layer which 
gradually hardens under pressure to become rock. This is 
called sedimentary rock, or stratified rock, because it is 
composed of sediment, and sediment always arranges itself 
in layers or strata. In sedimentary or stratified rocks 
fossils are found. The commonest rocks of this sort are 
limestone, sandstone, and shales. Limestone is formed 
chiefly of carbonate of lime ; sandstone is cemented sand ; 
and shales, or slaty rocks, are formed chiefly of clay. 

337. Sedimentary rocks. — The formation of sedimentary 
rocks has been going on since land first rose from the level 
of the sea ; for water has always been wearing away rock 
and carrying it as sediment into rivers, and rivers have 
always been carrying the worn-off lime and sand and clay 
downward to lakes and oceans, at the bottoms of which the 
particles have been piled up in layers and have formed new 
rock strata. But geologists have shown that in the course 
of the earth's history there have been great changes in the 
position and extent of land and sea. Sea-bottoms have 
been folded or upheaved to form dry land, while regions 
once land have sunk and been covered by lakes and seas. 
Again, through great foldings in the cooling crust of the 
earth, which resulted in depression at one point and eleva- 
tion at another, land has become ocean and ocean land. 
And in the almost unimaginable period of time which has 
passed since the earth first shrank from its condition of^ 
nebulous vapor to be a ball of land covered with water such 
changes have occurred over and over again. They have, 
however, all taken place slowly and gradually. The princi- 
pal seat of great change is in the regions of mountain 
chains, which, in most cases, are simply the remains of old 
folds or wrinkles in the crust of the earth. 

338. Deposition of fossils. — Xow we may see how fossils 
come to exist in the sedimentary rocks. "When an aquatic 
animal dies it sinks to the bottom of the lake or ocean, un- 
less, of course, its flesh is eaten by some other animal. 



THE ANIMALS OF THE PAST 423 

Even then its hard parts will probably find their way to the 
bottom. At the bottom the remains will soon be covered 
by the always dropping sediment. They are on the way to 
become fossils. Some land animals also might, after 
death, get carried by a river to the lake or ocean, and find 
their way to the bottom, where they, too, will become 
fossils. Or they may die on the banks of the lake or ocean 
and their bodies may get bnried in the soft mnd of the 
shores. Or, again, they are often trodden in the mire 
abont salt springs or submerged in quicksands. It is ob- 
vious that aquatic animals are far more likely to be pre- 
served as fossils than land animals. This inference is 
strikingly proved by fossil remains. Of all the thousands 
and thousands of kinds of extinct insects, mostly land 
animals, comparatively few 
specimens are known as fos- 
sils. On the other hand, 
the shell-bearing mollusks 
and crustaceans are repre- 
sented in almost all rock 
deposits which contain any 
kind of fossil remains. 

It is obvious that any por- 
tion Of the earth's Surface Fig. 244.— A fossil brachiopod {Spirifer 

covered by stratified rocks ITZZl^T^' ^ meaSUreS ' 
must have been at some time 

under water, the bottom of a lake or ocean. If now this 
portion shows a series of layers or strata of different kinds 
of sedimentary rocks, it is evident that it must have been 
under water several times, or at least under different con- 
ditions. It is also evident that fossils found in this portion 
of the earth will contain remains of only those animals 
which were living at the various times this portion of the 
earth was under water. Of the animals which lived on it 
when it was land, there will be no trace, except, possibly, a 
few land or fresh-water forms which might be swept into the 




424: 



ANIMAL STUDIES 



sea or might be preserved in the mud of small ponds. 
That is, instead of finding in the stratified rocks of any 
portion of the earth remains of all the animals which have 
lived on that portion since the earth began, we shall find, at 
best, only remains of a few kinds of those animals which 
have lived on this portion of the earth when it was covered 
by the ocean or by a great lake. 

339. Geological epochs and their animals.— Thus, the 
great body of fossil remains of animals reveal only a broken 
and incomplete history of the animal life of the past. But 

the record, so far as it 
goes, is an absolutely 
truthful one, and when 
the many deposits of fossils in all parts 
of the different continents are examined 
and compared, it is possible to state nu- 
merous general truths in regard to past 
life and the succession of animals in time. 
The science of extinct life is known as 
paleontology. 

The study of Paleontology has revealed 
much of the history of the earth and its 
inhabitants from the first rise of the land 
from the sea till the present era. This 
whole stretch of time — how long nobody 
knows — is divided into eras or ages ; these 
ages usually into lesser divisions called periods, and the 
periods into shorter lengths of time called epochs. Each 
epoch is more or less sharply distinguished from every 
other by the different species of animals and plants which 
lived while its rocks were being deposited. In the earth's 
crust, where it has not been distorted by foldings and 
breaks, the oldest stratified rocks lie at the bottom of the 
series, and the newest at the top. The fossils found in 
the lowest or oldest rocks represent, therefore, the oldest 
or earliest animals, those in the upper or newest rocks 




Fig. 245.— A Pterodac- 
tyl or flying reptile 
{Rhamphorhynchm 
gemmingi), Jurassic 
of Bavaria. — After 
Zittel. 



THE ANIMALS OF THE PAST 



425 



the newest or latest animals. An examination of a whole 
series of strata and their fossils shows that what we call 
the most specialized or most highly organized animals did 
not exist in the earliest epochs of the earth's history, but 




Fig. 246.— An Ostracoderm {Pterichyodes milleri), Lower Devonian of Scotland. — 
After Traqtjair. (The jointed appendage on the head is not a limb.1 

that the animals of these epochs were all of the simpler or 
lower kinds. For example, in the earlier stratified rocks 
there are no fossil remains of the backboned or vertebrate 
animals. When the vertebrates do appear, through several 
geological epochs they are fishes only, members of the low- 
est group of backboned animals. More than this, they 
represent generalized types of fishes which lack many of 




Fig. 247.— An Arthrodire {Cocc&steus decipiens), Lower Devonian of Scotland.— After 
Woodward. 

the special adaptations to marine life that modern fishes 
show. For this reason, they bear a greater resemblance to 
the earlier reptiles than do the fishes of to-day. In other 
words, they were a generalized type, showing the begin- 
nings of characters of their own and other types. It is 
always through generalized types that great classes of 
animals approach each other. 
28 



426 



ANIMAL STUDIES 



In a later epoch the batrachians or amphibians appeared ; 
in a still later period, the reptiles ; and last of all, the birds 
and the mammals, the last being the highest of the back- 
boned animals. On the opposite page is shown a table 
giving the names and succession of the various geological 
periods, and indicating briefly some of the kinds of animals 




Fig. 248.— A Crossopterygian fish (Osteolepis macrolepidotus). Devonian of Scotland.— 
From Zittel, after Pauder. 

living in each. In each of these divisions of geological 
time some one class of animals was especially numerous 
in species, and was evidently the dominant group of animals 
through that period. The different ages are therefore 
spoken of in terms of the prevailing life. Thus, the Silurian 
Age is known as the age or era of invertebrates ; the De- 
vonian, as the age of fishes. In the same way we have the 




Fig. 249.— Cladoselache fyleri (Newberry).— After Dean, from Devonian rocks in Ohio. 
The most primitive of known sharks. 

Reptilian Age, the Mammalian Age, according to the great 
class of animals predominating at that time. Of course, in 
each of the later epochs there lived animals representing 
the principal classes or groups in all of the preceding ones, 
as well as the animals of that particular group which may 
have first appeared in this epoch, or was its dominant group. 



THE ANIMALS OF THE PAST 



427 



Ages. 


Eras. 


Animals especially characteristic of 
the age or epoch. 


Cenozoic. 
Age of Mammals. 


Quaternary or 

Pleistocene 
(era of man and 

insects). 

( Pliocene 
Tertiary -j Miocene 
( Eocene 


Man ; the mammals mostly of 
species still living. 


Mammals abundant; belong- 
ing to numerous extinct 
families and orders. 




Cretaceous. 

Jurassic. 
Triassic. 


Bird-like reptiles; flying rep- 
tiles; toothed birds; first 
snakes ; bony fishes. 


Mesozoic. 
Age of Reptiles. 


First birds ; giant reptiles ; am- 
monites; clams and snails 
abundant. 




First mammals (a marsupial, 
lowest kind of mammals). 




Carboniferous 
(era of amphibians). 

Devonian 
(era of fishes). 

Silurian 
(era of inverte- 
brates). 

Ordovician or 
Lower Silurian. 

Cambrian. 


Earliest true reptiles. 
Amphibians. 
First crayfishes ; insects 
- abundant; spiders; fresh- 
water mussels. 


Paleozoic. 
Age of Inverte- 
brates. 


First amphibian (frog-like 
animals) ; cartilaginous fish- 
es, shark-like or mailed ; first 
land shells (snails); shell-fish 
abundant ; first crabs. 


First truly terrestrial or air- 
breathing animals; first in- 
sects ; corals abundant; 
mailed fishes. 




First fishes, probably shark- 
like with cartilaginous skele- 
ton : brachiopods ; trilobites, 
mollusks, etc. 




Invertebrates only. 


Archeax. 


Algonkian. 
Laurentian. 


Simple marine invertebrates. 



428 



ANIMAL STUDIES 



But certain subdivisions of a principal group or class of 
animals often appear in an early epoch, become very abun- 
dant and highly specialized in a later one, and almost 
wholly or even totally disappear in a still later one. For ex- 
ample, a group of certain curious animals called Trilobites 
(Fig. 250), belonging to the great class Crustacea (which 
includes the crabs, crayfishes, and lobsters), first appeared in 




Fig. 250.— Cambrian Trilobites. a, Paracloxides Bohemicus, reduced in size ; b, Ellip- 
s cephalus Hoffi; c, Sao hirsuta; d, Conocoryphe Sultzeri (all the above, together 
with Fig. g, are from the Upper Cambrian or "primordial zone" of Bohemia); 
e, head-shield of Dikellocephalus Celticus, from the Lingula flags of Wales; 
/, head-shield of Conocoryphe Matthewi, from the Upper Cambrian (Acadian 
group) of New Brunswick; g, Agnostus rex, Bohemia; h, tail-shield of Dikello- 
cephalus Mnnesotensis, from the Upper Cambrian (Potsdam sandstone) of Minne- 
sota.— From Nicholson, after Barrande. Dawson, Salter, and Dale Owen. 

the Cambrian era, became very abundantly represented in the 
Silurian era, began to decline in the Devonian, and became 
extinct in the Carboniferous era. This was not the extinc- 
tion of a single kind or species of animal, but of a large 



THE ANIMALS OF THE PAST 429 

group of animals represented by thousands of species. 
Another group with a similar history, traced out wholly by 
the study of fossils, is that of the sea-lilies or crinoids, 
radiate animals fixed by a stalk to the bottom, in struc- 
ture resembling starfishes and sea-urchins. By the abun- 





Fig. 251. — Ammonite {Ammonites humphresianus) from the Jurassic of Europe. — 
After Nicholson. 

dance and variety of their remains, it is evident that at one 
time in the earth's history the crinoids were an important 
and flourishing group of animals. At present, however, 
there are but very few known living species of crinoids, and 
these are found only in the unchanging conditions of great 
depths in the sea. Again, the Nautilus is the only living 
near relative of what was, in Mesozoic time, a group with 
hosts of species, the Ammonites (Fig. 251) bearing coiled 
shells, often very elaborately ornamented. 

340. Man. — The first traces of man appear in the later geo- 
logic epochs in the period called Tertiary. Human bones 
have been found in caves together with those of the cave- 
lion, cave-bear, and other extinct animals. In certain lakes 
in Switzerland and Austria have been found remains of 
peculiar dwellings, together with ancient fishing-hooks and 



430 ANIMAL STUDIES 

a variety of implements of stone and bronze. These houses 
were built on piles in the lakes, and connected with the 
shore by long piers or bridges. The extinct race of men 
who lived in them are known as lake-dwellers. Eelics of 
man, especially rough stone tools and flint arrow- and axe- 
heads, and skulls and other bones, have been found under 
circumstances which indicate with certainty that man has 
existed long on the earth. In Java are found some ancient 
bones of man-like animals {Pithecanthropus and Anthro- 
pithecus), different, however, from any species or race of 
men living to-day, and showing traits which indicate a 
closer relationship with lower animals. The time of his- 
toric man — i. e., the period which has elapsed since the 
history of man can be traced from carvings or buildings or 
writings made by himself — is short indeed compared with 
that of prehistoric man. Barbarous man writes no history 
and leaves no record save his tools and his bones. Iron 
and bronze rust, bones decay, w r ood disappears. Only stone 
implements remain to tell the tale of primitive humanity. 
These give no exact record of chronology. 

So of the actual duration of man's prehistoric existence 
we can make no estimate. Speaking in terms of the earth's 
history, man is very recent, the latest of all the animals. 
In terms of the history of man, he is very ancient. The 
exact records of human history cover only the smallest 
fraction of the period of man's existence on earth. 

341. Light thrown on zoology by paleontology. — It is 
plain that much is to be learned, especially in regard to 
the relationships existing among living animals, by a study 
• of those of the past. A comparison of certain of the ancient 
reptiles with the long-tailed Archmopteryx (Fig. 252) and 
other toothed birds show that the birds and reptiles were 
once scarcely distinguishable, although now so very differ- 
ent. Birds have feathers, reptiles do not ; and there is 
scarcely any other permanent resemblance. Fossils show a 
similar close relation between amphibians and fishes. A 



THE ANIMALS OF THE PAST 431 

study of these ancient forms also throws light on many 
conditions of structure in modern animals otherwise diffi- 
cult to understand. For example, while most of the ani- 
mals closely related to the horse have five toes on each of 
their feet, the horse has only one. We know that the leg 



Fig. 252.— Saurian bird with jointed tail, claws on wings, and teeth in jaws (Archce- 
opteryx lithographica), from the Jurassic rocks of ^avaria.— After Nicholson, 
from Owen. 

and foot of a horse are homologous with the leg and foot 
of a dog, yet a dog's foot has five (on the hind foot usually 
four) toes, while the horse's foot has never more than one 
toe. But the study of the ancient horses makes all this 
clear. The remains of over thirty different ancient horse- 
like animals have been found in the rocks of the Tertiary 
era. The Eohippus, the earliest of these horse-like animals, 
found in the oldest Tertiary rocks, was little larger than a 
fox, and its fore feet had four hoofed toes, with the rudi- 
ment of a fifth, while the hind feet had three hoofed toes 
(Fig. 253). 

In later rocks is found the OroMppus, also small, 
but with the rudimentary fifth toe of the fore foot gone. 
Still later appeared the MesoMppus and Miohippus, horses 
about the size of sheep, with three hoofed toes only on both 



432 ANIMAL STUDIES 

fore feet and hind feet, but with the rudiment of the fourth 
toe in the fore feet, of the same size in 3£esohippus, smaller 
in Miohippus. Also, the middle toe and hoof of the three 
toes in each foot was distinctly larger than the others in. 
both Mesohippus and Miohippus. Next came the Proto- 
hippus, a horse about the size of a donkey, with three toes, 
but with the two side toes on each foot reduced in size, and 
probably no longer of use in walking. The middle toe and 
hoof carried all the weight. Still later in the Tertiary era 




Fig. 253.— Extinct four-toed horse (Eohippus) from the Eocene of Wyoming, 16 
inches high.— After W. D. Matthew, painting by C. R. Kkight. 

lived the Pliohippus, an " almost complete horse." The side 
toes of Plioliippus are reduced to mere rudiments or splints. 
This animal differs from the present horse somewhat in 
skull, shape of hoof, length of teeth, and other minor de- 
tails. Lastly came the present horse, Equus, with the 
splint bones or concealed rudiments of the side toes very 



THE ANIMALS OF THE PAST 



433 



small, and the hoof of the middle toe rounder. In spite of 
the great difference between the one-toed foot of the living 
horse and the dog's five-toed foot, there was once a kind of 
horse which had a five-toed 
foot, and there is after all a 
close relationship between 
the foot of the horse and 
the foot of the dog. 

342. Parallelism of em- 
bryonic stages with fossil 
series. — One of the most im- 
portant truths of paleon- 
tology is that the ancient 
groups in any type agree 
more or less closely in 
structure with the embryos 
or with the larval stages of 
the living representatives of 
the same group. Embryos 
are generalized organisms 
simple in structure as com- 
pared with the adult ani- 
mal. The earlier represen- 
tatives of any class or type 

of animal are likewise simple and devoid of specializa- 
tion. And there is a curious parallelism, which is not 
accidental, in the resemblance in the successive stages of 
animal life in a series of fossils to the successive stages in 
the embryo of recent forms. The persistence of heredity 
is undoubtedly the cause of this parallelism. By its influ- 
ence ancestral traits are repeated in the embryo, even 
though the characters thus produced give way in later 
development to further specialization or growth along 
other lines. This great truth has been stated in these 
words : " The life-history of the individual is an epitome 
of the life-history of the group to which it belongs." This 




Fig. 254. —Feet in fossil pedigree of horse. 
—After Marsh, a, Equus, Quaternary 
(recent) ; b, Pliohippus, Pliocene ; c, 
Protohippus, Lower Pliocene ; d, Mio- 
hippus, Miocene; e, Mesohippus, Lower 
Miocene ; /, Orohippus, Eocene. 



434 ANIMAL STUDIES 

statement is only true when stated very broadly, for there 
are many exceptions or modifications. The embryonic or 
larval animal is subject to almost endless secondary changes 
and adaptations whenever these changes are for the advan- 
tage of the animal. In general, the simpler the structure 
of the animal and the less varied its relations in life, the 
more perfectly are these ancient phases of heredity pre- 
served in the process of development. In such case, the 
more perfect the parallelism between the development of 
the individual and the succession of forms in geologic time. 



CHAPTEE XXIX 

GEOGRAPHICAL DISTRIBUTION OF ANIMALS 

343. Geographical distribution. — Under the head of dis- 
tribution we consider the facts of the diffusion of organ- 
isms over the surface of the earth, and the laws by which 
this diffusion is governed. 

The geographical distribution of animals is often known 
as zoogeography. In physical geography we may prepare 
maps of the earth which shall bring into prominence the 
physical features of its surface. Such maps would show 
here a sea, here a plateau, here a range of mountains, 
there a desert, a prairie, a peninsula, or an island. In po- 
litical geography the maps show the physical features of 
the earth, as related to the states or powers which claim 
the allegiance of the people. In zoogeography the realms 
of the earth are considered in relation to the types or 
species of animals which inhabit them. Thus a series of 
maps of the United States could be drawn which would 
show the gradual disappearance of the buffalo before the 
attacks of man. Another might be drawn which would 
show the present or past distribution of the polar bear, 
black bear, and grizzly. Still another might show the 
original range of the wild hares or rabbits of the United 
States, the white rabbit of the Northeast, the cotton-tail of 
the East and South, the jack-rabbit of the plains, the snow- 
shoe rabbit of the Columbia Eiver, the tall jack-rabbit of 
California, the black rabbits of the islands of Lower Cali- 
fonia, and the marsh-hare of the South and the water-hare 
of the canebrakes, and that of all their relatives. Such a 

435 




Fig. 255.— Map showing the distribution of the clouded Skipper butterfly (Lerema 
accius) in the United States. The butterfly is found in that part of the country 
shaded in the map, a warm and moist region.— After Scuddek. 



o 

Cl 1 

/ \ 


V* D o' 115 M. 

c 4 \>- — L£oto 


_^0 F C A I N| A D 'y^T [yJlP 


J v (ill. indI" Ac^Mjo tv & 

KAN. f MOX^/p ^L^ 


o 
o 

-30 , 


■Wx 

"XA v e x. 

T \\ \ T 


^ /.? ALA.\ ^X/ " 

tex n« Li I w 

pSlj=6r~\ ** ERYNNIS 
~"\ y—^S^ y<A ^ MANITOBA 

\ (aVLT of MEX1C0\'\ 

V~J 95 65 \ 75 65 
^ 1 1 *■» 1 \ 



Fig. 256.— Map showing: the distribution of the Canadian Skipper butterfly (Erynnis 
manitoba) in the United States. The butterfly is found in that part of the 
country shaded in the map. This butterfly is subarctic and subalpine in dis- 
tribution, being found only far north or on hicrh mountains, the two southern 
projecting- parts of its range being in the Kocky Mountains and in the Sierra 
Nevada Mountains.— After Scuddbr. 
436 



GEOGRAPHICAL DISTRIBUTION OF ANIMALS 437 

map is very instructive, and it at once raises a series of 
questions as to the reasons for each of the facts in geo- 
graphical distribution, for it is the duty of science to sup- 
pose that none of these facts is arbitrary or meaningless. 
Each fact has some good cause behind it. 

344. Laws of distribution. — The laws governing the dis- 
tribution of animals are reducible to three very simple 
propositions. Every species of animal is found in every part 
of the earth having conditions suitable for its maintenance, 
unless — 

(a) Its individuals have been unable to reach this re- 
gion, through barriers of some sort; or — 

(b) Having reached it, the species is unable to maintain 
itself, through lack of capacity for adaptation, through 
severity of competition with other forms, or through de- 
structive conditions of environment ; or — 

(c) Having entered and maintained itself, it has become 
so altered in the process of adaptation as to become a spe- 
cies distinct from the original type. 

345. Species debarred by barriers. — As examples of the 
first class we may take the absence of kingbirds or meadow- 
larks or coyotes in Europe, the absence of the lion and 
tiger in South America, the absence of the civet-cat in New 
York, and that of the bobolink or the Chinese flying-fox in 
California. In each of these cases there is no evident rea- 
son why the species in question should not maintain itself 
if once introduced. The fact that it does not exist is, in 
general, an evidence that it has never passed the barriers 
which separate the region in question from its original 
home. 

Local illustrations of the same kind may be found in 
most mountainous regions. In the Yosemite Valley in 
California, for example, the trout ascend the Merced Eiver 
to the base of a vertical fall. They can not rise above this, 
and so the streams and lakes above this fall are destitute 
of fish. 



438 ANIMAL STUDIES 

346. Species debarred by inability to maintain their ground. 
— Examples of the second class are seen in animals that 
man has introduced from one country to another. The 
nightingale, the starling, and the skylark of Europe have 
been repeatedly set free in the United States. But none of 
these colonies has long endured, perhaps from lack of adap- 
tation to the climate, more likely from severity of competi- 
tion with other birds. In other cases the introduced species 
has been better fitted for the conditions of life than the 
native forms themselves, and so has gradually crowded out 
the latter. Both these cases are illustrated among the rats. 
The black rat, first introduced into America from Europe 
about 1544, helped crowd out the native rats, while the 
brown rat, brought in still later, about 1775, in turn practi- 
cally exterminated the black rat, its fitness for the condi- 
tions of life here being still greater than that of the other 
European species. 

347. Species altered by adaptation to new conditions. — 
Of the third class or species altered in a new environment 
examples are numerous, but in most cases the causes in- 
volved can only be inferred from their effects. One class 
of illustrations maybe taken from island faunae. An island 
is set off from the mainland by barriers which species of 
land animals can very rarely cross. On an island a few waifs 
of wave and storm may maintain themselves, increasing in 
numbers so as to occupy the territory; but in so doing 
only those will survive that can fit themselves to the new 
conditions. Through this process a new species will be 
formed, like the parent species in general structure, but 
having gained new traits adjusted to the new environ- 
ment. 

To processes of this kind, on a larger or smaller scale, 
the variety in the animal life of the globe is very largely 
due. Isolation and adaptation give the clew to the forma- 
tion of a very large proportion of the " new species " in 
any group. 



GEOGRAPHICAL DISTRIBUTION OF ANIMALS 439 



" 




m- 



Fig. 257.— On the shore of Narborough Island, one of the Galapagos Islands, Pacific 
Ocean, showing peculiar species of sea-lions, lizards, and cormorants. Drawn 
from a photograph made by Messrs. Snodgrass and Heller. 



348. Effect of barriers. — It will be thus seen that geo- 
graphical distribution is primarily dependent on barriers or 
checks to the movement of animals. The obstacles met 
in the spread of animals determine the limits of the spe- 
cies. Each species broadens its range as far as it can. It 



440 ANIMAL STUDIED 

attempts unwittingly, through natural processes of n^-rease, 
to overcome the obstacles of ocean or river, of mountain or 
plain, of woodland or prairie or desert, of cold or heat, of 
lack of food or abundance of enemies — whatever the bar- 
riers may be. Were it not for these barriers, each type or 
species would become cosmopolitan or universal. Man is 
preeminently a barrier-crossing animal ; hence he is found 
in all regions where human life is possible. The different 
races of men, however, find checks and barriers entirely 
similar in nature to those experienced by the lower animals, 
and the race, peculiarities are wholly similar to characters 
acquired by new species under adaptation to changed con- 
ditions. The degree of hindrance offered by any barrier 
differs with the nature of the species trying to surmount it. 
That which constitutes an impassable obstacle to one form 
may be a great aid to another. The river which blocks the 
monkey or the cat is the highway of the fish or the turtle. 
The waterfall which limits the ascent of the fish is the 
chosen home of the ouzel. The mountain barrier which 
the bobolink or the prairie-dog does not cross may be the 
center of distribution of the chief hare or the arctic blue- 
bird. 

349. Fauna andfaunal areas. — The term fauna is applied 
to the animals of any region considered collectively. Thus 
the fauna of Illinois comprises the entire list of animals 
found naturally in that State. It includes the aboriginal 
men, the black bear, the fox, and all its animal life down 
to the Amoeba. The relation of the fauna of one region 
to that of another depends on the ease with which bar- 
riers may be crossed. Thus the fauna of Illinois differs 
little from that of Indiana or Iowa, because the State con- 
tains no barriers that animals may not readily pass. On 
the other hand, the fauna of California or Colorado differs 
materially from that of adjoining regions, because a moun- 
tainous country is full of barriers which obstruct the diffu- 
sion of life. Distinctness is in direct proportion to isola- 



GEOGRAPHICAL DISTRIBUTION OF ANIMALS 441 

tion. What is true in this regard of the fauna of any region 
is likewise true of its individual species. The degree of 
resemblance among individuals is in strict proportion to 
the freedom of their movements. Variation within the 
limits of a species is again proportionate to the barriers 
which prevent equal and free diffusion. 

350. Realms of animal life. — The various divisions 01 
realms into which the land surface of the earth may be 
divided on the basis of the character of animal life have 
their boundary in the obstacles offered to the spread of the 
average animal. In spite of great inequalities in this regard^ 
we may yet roughly divide the land of the globe into seven 
principal realms or areas of distribution, each limited by 
barriers, of which the chief are the presence of the sea and 
the occurrence of frost. There are the Arctic, North Tem- 
perate, South American, Indo-African, Lemurian, Patago- 
nian, and Australian realms. Of these the Australian 
realm alone is sharply defined. Most of the others are sur- 
rounded by a broad fringe of debatable ground that forms 
a transition to some other zone. 

The Arctic realm includes all the land area north of the 
isotherm of 32°. ' Its southern boundary corresponds closely 
with the northern limit of trees. The fauna of this region 
is very homogeneous. It is not rich in species, most of the 
common types of life of warmer regions being excluded. 
Among the large animals are the polar bear, the walrus, and 
certain species of " ice-riding " seals. There are a few spe- 
cies of fishes, mostly trout and sculpins, and a few insects ; 
some of these, as the mosquito, are excessively numerous 
in individuals. Eeptiles are absent from this region and 
many of its birds migrate southward in the winter, finding 
in the arctic only their breeding homes. "When we consider 
the distribution of insects and other small animals of wide 
diffusion we must add to the arctic realm all high moun- 
tains of other realms whose summits rise above the timber 
line. The characteristic large animals of the arctic, as the 
29 



442 ANIMAL STUDIES 

polar bear or the musk-ox or the reindeer, are not found 
there, because barriers shut them off. But the flora of the 
mountain top, even under the equator, may be character- 
istically arctic, and with the flowers of the north may be 
found the northern insects on whose presence the flower 
depends for its fertilization. So far as climate is concerned 
high altitude is equivalent to high latitude. On certain 
mountains the different zones of altitude and the corre- 
sponding zones of plant and insect life are very sharply 
defined. 

The North Temperate realm comprises all the land be- 
tween the northern limit of trees and the southern limit of 
frost. It includes, therefore, nearly the whole of Europe, 
most of Asia, and most of North America. While there 
are large differences between the fauna of Xorth America 
and that of Europe and Asia, these differences are of minor 
importance, and are scarcely greater in any case than the 
difference between the fauna of California and that of our 
Atlantic coast. The close union of Alaska with Siberia 
gives the arctic region an almost continuous land area from 
Greenland to the westward around to Xorway. To the 
south everywhere in the temperate zone realm the species 
increase in number and variety, and the differences between 
the fauna of Xorth America and that of Europe are due in 
part to the northward extension into the one and the other 
of types originating in the tropics. Especially is this true 
of certain of the dominant types of singing birds. The 
group of wood-warblers, tanagers, American orioles, vireos, 
mocking-birds, with the fly-catchers and humming-birds so 
characteristic of our forests, are unrepresented in Europe. 
All of them are apparently immigrants from the neotropical 
realm where nearly all of them spend the winter. In the 
same way central Asia has many immigrants from the Indian 
realm to the southward. "With all these variations there 
is an essential unity of life over this vast area, and the rec- 
ognition of Xorth America as a separate (nearctic) realm, 



GEOGRAPHICAL DISTRIBUTION OF ANIMALS 443 

which some writers have attempted, seems hardly practi- 
cable. 

The Neotropical or South American realm includes 
South America, the West Indies, the hot coast lands of 
Mexico, and those parts of Florida and Texas where frost 
does not occur. Its boundaries through Mexico are not 
sharply defined, and there is much overlapping of the north 
temperate realm along its northern limit. Its birds espe- 
cially range widely through the United States in the sum- 
mer migrations, and a large part of them find in the North 
their breeding home. Southward, the broad barrier of the 
two oceans keeps the South American fauna very distinct 
from that of Africa or Australia. The neotropical fauna is 
richest of all in species. The great forests of the Amazon 
are the dreams of the naturalists. Characteristic types 
among the larger animals are the snout or broad-nosed 
(platyrrhine) monkeys, which in many ways are very distinct 
from the monkeys and apes of the Old World. In many of 
them the tip of the tail is highly specialized and is used as 
a hand. The Edentates (armadillos, ant-eaters, etc.) are 
characteristically South American, and there are many 
peculiar types of birds, reptiles, fishes, and insects. 

The Indo- African realm corresponds to the neotropical 
realm in position. It includes the greater part of Africa, 
merging gradually northward into the north temperate 
realm through the transition districts which border the 
Mediterranean. It includes also Arabia, India, and the 
neighboring islands, all that part of Asia south of the limit 
of frost. In monkeys, carnivora, ungulates, and reptiles 
this region is wonderfully rich. In variety of birds, fishes, 
and insects the neotropical realm exceeds it. The monkeys 
of this district are all of the narrow-nosed (catarrhine) 
type, various forms being much more nearly related to 
man than is the case with the peculiar monkeys of South 
America. Some of these (anthropoid apes) have much 
in common with man, and a primitive man derived from 



444 



ANIMAL STUDIES 



these has been imagined by Haeckel and others. Xo 
creature of this character is yet known, but that it may 
have once existed is not impossible. To this region be- 
long the elephant, the rhinoceros, and the hippopotamus, 
as well as the lion, tiger, leopard, giraffe, the wild asses, 
and horses of various species, besides a large number of 
ruminant animals not found in other parts of the world. 
It is, in fact, in its lower mammals and reptiles that its 
most striking distinctive characters are found. In its fish 
fauna it has very much in common with South America. 

The Lemurian realm comprises Madagascar alone. It is 
an isolated division of the Indo- African realm, but the pres- 
ence of many spe- 
cies of lemur and 
an unspecialized or 
primitive type of 
lemur is held to 
justify its recogni- 
tion as a distinct 
realm. In most 
other groups of 
animals the fauna 
of Madagascar is 
essentially that of 
neighboring joarts 
of Africa. 

The Patagonia n 
realm includes the 
south temperate 
zone of South Amer- 
ica. It has much 
in common with the 
neotropical realm from which its fauna is mainly derived, 
but the presence of frost is a barrier which vast numbers 
of species can not cross. Beyond the Patagonian realm 
lies the Antarctic continent, The scanty fauna of this 




Fig. 258.— A lemur (Lemur varius). 



GEOGRAPHICAL DISTRIBUTION OF ANIMALS 445 

region is little known, and it probably differs from the 
Patagonian fauna chiefly in the absence of all but the ice- 
riding species. 

The Australian realm comprises Australia and the 
neighboring islands. It is more isolated than any of the 
others, having been protected by the sea from the invasions 
of the characteristic animals of the Indo- African and tem- 
perate realms. It shows a singular persistence of low or 
primitive types of vertebrate life, as though in the process 
of evolution the region had been left a whole geological 
age behind the others. It is certain that if the closely 
competing fauna of Africa and India could have been able 
to invade Australia, the dominant mammals and birds of 
that region would not have been left as they are now — mar- 
supials and parrots. 

It is only when barriers have shut out competition that 
simple or unspecialized types abound. The larger the land 
area and the more varied its surface, the greater is the 
stress of competition and the more specialized are its char- 
acteristic forms. As part of this specialization is in the 
direction of hardiness and power to persist, the species from 
the large areas, as a whole, are least easy of extermination. 
The rapid multiplication of rabbits and foxes in Australia, 
when introduced by the hand of man, shows what might 
have taken place in this country had not impassable barriers 
of ocean shut them out. 

351. Subordinate realms or provinces. — Each of these great 
realms may be indefinitely subdivided into provinces and 
sections, for there is no end to the possibility of analy- 
sis. No school district has exactly the same animals or 
plants as any other, as finally in ultimate analysis we find 
that no two animals or plants are exactly alike. Shut off 
one pair of animals from the others of its species, and its 
descendants will differ from the parent stock. This differ- 
ence increases with time and with distance so long as the 
separation is maintained. Hence new species and new 



446 ANIMAL STUDIES 

fauna or aggregations of species are produced wherever 
free diffusion is checked by any kind of barrier. 

352. Faunal areas of the sea. — In like manner, we may 
divide the oceans into faunal areas or zones, according to 
the distribution of its animals. For this purpose the fishes 
probably furnish the best indications, although results very 
similar are obtained when we consider the mollusks or the 
Crustacea. 

The pelagic fishes are those which inhabit the open sea, 
swimming near the surface, and often in great schools. 
Such forms are mainly confined to the warmer waters. 
They are for the most part predatory fishes, strong swim- 
mers, and many of the species are found in all warm seas. 
Most species have special homing waters, to which they 
repair in the spawning season. To the free-swimming forms 
of classes of animals lower than fishes, found in the open 
ocean, the name Plankton is applied. 

The bassalian fauna, or deep-sea fauna, is composed of 
species inhabiting great depths (2,500 feet to 25,000 feet) 
in the sea. At a short distance below the surface the 
change in temperature from day to night is no longer felt. 
At a still lower depth there is no difference between winter 
and summer, and still lower none between day and night. 
The bassalian fishes inhabit a region of great cold and inky 
darkness. Their bodies are subjected to great pressure, 
and the conditions of life are practically unvarying. There 
is therefore among them no migration, no seasonal change, 
no spawning season fixed by outside conditions, and no 
need of adaptation to varying environment. As a result, all 
are uniform indigo-black in color, and all show more or 
less degeneration in those characters associated with ordi- 
nary environment. Their bodies are elongate, from the 
lack of specialization in the vertebrae. The flesh, being 
held in place by the great pressure of the water, is soft and 
fragile. The organs of touch are often highly developed. 
The eye is either excessively large, as if to catch the slight- 



GEOGRAPHICAL DISTRIBUTION OF ANIMALS 447 



est ray of light, or else it is undeveloped, as if the fish had 
abandoned the effort to see. In many cases luminous spots 
or lanterns are developed by which the fish may see to 
guide his way in the sea, 
and in some forms these 
shining appendages are 
highly developed. In one 
form {JEtho2orora) a lumi- 
nous body covers the end 
of the nose, like the head- 
light of an engine. In an- 
other (Ipnops) the two eyes 
themselves are flattened 
out, covering the whole top 
of the head, and are lumi- 
nous in life. Many of 
these species have exces- 
sively large teeth, and some 
have been known to swal- 
low animals actually larger 
than themselves. Those 
which have lantern -like 
spots have always large 
eyes. 

The deep-sea fishes, 
however fantastic, have all 
near relatives among the 
shore forms. Most of them are degenerate representatives 
of well-known species — for example, of eels, cod, smelt, 
grenadiers, sculpin, and flounders. The deep-sea crusta- 
ceans and mollusks are similarly related to shore forms. 

The third great subdivision of marine animals is the 
littoral or shore group, those living in water of moderate 
depth, never venturing far into the open sea either at the 
surface or in the depths. This group shades into both 
the preceding. The individuals of some of the species are 




Fig. 259.— A crinoid (Shizocrinus loxoteri' 
sis). A deep-sea animal which lives, 
fixed plant-like, at the bottom of the 
ocean. 



448 ANIMAL STUDIES 

excessively local, remaining their life long in tide pools or 
coral reefs or piles of rock. Others venture far from home, 
and might well be classed as pelagic. Still others ascend 
rivers either to spawn (anadromous, as the salmon, shad, 
and striped bass), or for purposes of feeding, as the robalo, 
corvina, and other shore-fishes of the tropics. Some live 
among rocks alone, some in sea-weed, some on sandy shores, 
some in the surf, and some only in sheltered lagoons. In 
all seas there are fishes and other marine animals, and 
each creature haunts the places for which it is fitted. 



INDEX 



Actitix maeularia, 223. 

Adamsia palliata (illus.), 338. 

Adaptations, origin of, 290 ; classifi- 
cation of, 290 ; for securing food, 
292 ; for self-defense, 294 ; for ri- 
valry, 301 ; for the defense of the 
young, 302 ; concerned with sur- 
roundings in life, 308 ; degree of 
structural change in, 311. 

Adjustment to surroundings, S87. 

y&gialitis vocifera, 224. 

JEthoprora, 4A1. 

Agassiz's cave fish (illus.), 173. 

Air-bladder, 165. 

Albatrosses, 219. 

Albula vidpes, 272. 

Alligator lizard (illus.), 352. 

Alligator mississippiensis (illus.), 
199. 

Alligators (illus., 199), 198. 

Alluring coloration, 363. 

Alternation of generations, 49. 

Altricial nestlings of the blue jay 
(illus.), 303. 

Alytes, 190. 

Ambly stoma opacmn (illus.), 185 ; 
tigrinum (illus.), 186, 190, 191. 

American bittern, nestlings of (il- 
lus.), 393, ?94. 

Ammonite (illus.), 429. 

Ammonites humphresianus (illus.) 
429. 

Amoeba (illus.), 23 ; multiplication 
of by simple fission (illus.), 71, 
255, 372. 

Amphibians, 182. 

Amphipods (illus., 122), 131. 



Andrena (illus.), 325. 

Andricus californicus (illus.), 308. 

Anguillula (illus.), 68. 

Animal functions, 12. 

Animal life, conditions of, 1, 4; 
realms of, 441. 

Animal products used in the arts, 411 

Animals, families of, 17 ; higher 
groups of, 17; simplest, 22; sin- 
gle-celled, 22 ; simple and complex, 
31 : of uncertain relationships, 83 
crowd of, 281 ; domestic. 404 ; ser- 
vices of, 406 ; used as food, 406 
clothing from, 409 ; as ornaments, 
410; as enemies and destroyers, 
412 ; as servants, 415 ; as friends. 
415 ; of the past, 417 ; extinct, 
417; mammoth (illus.), 417; be- 
coming extinct, 419. 

Animals and plants, comparison of, L 

Anna hummer (illus.), 230, 231. 

Annelids, 72. 

Anosia plexippus (illus.), 141 ; (il- 
lus.), 268, 365. 

Ant-eaters, 443. 

Antedon (illus.), 158. 

Antennarius, 364. 

Anthropithectis, 430. 

Anthropopithecus, 250. 

Antilocapra amerlcana, 246. 

Ant-lions, 134, 135 (illus.), 136. 

Antrostomus vociferus, 230. 

Ants, 142 (illus.), 320. 

Aphidfe, 321. 

Aptera, 133. 

Aquila chryscetus, 226 (illus. ), 287. 

Arachnida, 110, 143. 
449 



450 



ANIMAL STUDIES 



Archceopteryx lithographica (illus.), 

431. 
Arctic realm, 441. 
Ardea herodias, 222 ; Ardea viris- 

cens, 222. 
Argynniscybele (illus.), 142. 
Ariolimax, 98. 
Armadillos, 443. 
Arnithorhynchus paradoxus (illus.), 

237. 
Arthrodire (illus.), 425. 
Arthropoda, 19. 
Arthropods, 109, 130. 
Articulata, 19. 
Artificial propagation, 406. 
Ascidians, 1G2. 
Asclepias, 268. 
Astacus (illus.), 117. 
Asterias ocracea (illus), 151. 
Astrophyton (illus.), 153. 
Ateles, 250. 
Aua, 333. 
Auks, 217. 

Australian duck-mole (illus), 237. 
Australian realm, 445. 
Axoloti (illus.), 190. 
Ay thy a (illus.), 302 

Band worms, 87 (illus.), 88. 

Barnacles (illus. 113), 112, 115 ; meta- 
morphosis of (illus.), 275. 

Barriers, effect of, 439. 

Bascanion constrictor (illus.), 195. 

Basilarchia airhippus, 365. 

Basket-star (illus.), 153 

Bassalian fauna, 446. 

Bats, 242. 

Beavers. 331. 

Bees, 142. 

Beetles, 140. 

Bell animalcule, 27. 

Birds, characteristics of, 209; molt- 
ing, 210 ; skeleton of, 212 ; inter- 
nal structures. 213; anatomy of 
(illus.), 213 ; digestive system. 214 ; 
nesting habits. 215 ; classification, 
217 ; prcecocial (illus.), 302. 305; 
altricial (illus.), 303, 305 ; extinct, 
419. 



Bison americanus, 246. 

Blacksnake (illus.), 195. 

Blastula (illus., 36), 35. 

Blindfish (illus.), 173. 

Blunt-nosed salamander (illus.), 185. 

Bob-white, 225. 

Boyiasa umbellus, 225. 

Bony fishes, 170; dissection of 

(illus.), 178. 
Box-turtle (illus.), 197. 
Brain or sensonum, 388. 
Brachiopods (illus., 86), S7. 
Brady pus (illus.), 2,36. 
Branchiostoma, 166; B. californu 

ense (illus.), 167. 
Branch ip us (illus., Ill), 110. 
Branta ca?iade?isis, 211 ; B, berni- 

cla, 221. 
Brittle or serpent-stars (illus.), 152. 
Brown pelican (illus.), 292. 
Bubo virginianus, 227. 
Buffalo, 246. 
Bugs, 137. 

Bumble bees, 324 (illus), 326. 
Bnteo borealis, 226 ; B. lineatus,226. 
Butterfly, 226 ; larva of (illus.), 270 ; 

chrysalid of (illus.), 354. 



Cabbage-butterfly, 367. 
Calcolynthus primigenius (illus.) 

39. 
Calf, tongue of (illus.), 376. 
California barn-door skate (illus.), 

305. 
California lancelet (illus.). 167. 
California quail (illus.). 2.4. 
California woodpecker (illus.), 294, 

295. 
Calypte a?ina (illus.). 231. 
Cambrian trilobites (illus.). 428. 
Camponotns sp. (illus.), 320. 
Canadian skipper butterfly. 436. 
Cancer productiM (illus ). 120. 
Canis latrans, 248; C. nubilus,'2A%\ 

C. familiar is, 248. 
Caprella (illus.). 122. 
Carnivora, 246. 
Carpenter-bee, nest of (illus.), 325. 



INDEX 



451 



Castor canadensis, 241. 

Castoridse, 17. 

Cat family, 248. 

Caterpillar, parasitized (illus.), 342. 

Catfishes, 172. 

Cathartes aura, 226. 

Cave blindfish (illus.), 173. 

Ceanothus moth, cocoon of (illus.), 
306. 

Cebus, 250. 

Cells, 9 ; different types of (illus.), 
11. 

Centiped (illus., 128), 127 (illus.), 
296. 

Cephalopods, 89 (illus., 105), 104. 

Ceratiidcc, 364. 

Cercopithecm (illus., 251), 250, 400. 

Centra (illus.;, 363. 

Cervidce, 245. 

Ceryle alcyon, 228. 

Cestodes, 65. 

Cete, 242. 

Chcetura pelagica, 230. 

Cheiroptera, 242. 

Chelonia, 196. 

Chipmunks of California (illus.), 20. 

Chiton (illus.), 99. 

Chologaster avitus (illus.), 73. 

Chordata, 19, 161. 

Chordei es virginianus (illus.), 229. 

Cilia, 27. 

Circus hudsonius, 226. 

Cladoselache fyleri (illus.), 426. 

Clams, 89; fresh-water (illus.), 91; 
rock- and wood-boring, 92 ; life his- 
tory of, 97. 

Classification, principles of, 13 ; nat- 
ural, 14. 

Clepsine, 82. 

Climate, 395. 

Cliona, 336. 

Coccidse, 321, 346. 

Coccosteus decipiens (illus.), 425. 

Coccyges, 227. 

Cockroach (illus.), 132 ; egg-case of 
(illus.), 305. 

Colaptes auratus, 228. 

Coleoptera, 140. 

Colinns virginianus, 225. 



Color ; its utility and beauty, 369. 
Columba livia, 225, 288. 
Columbse, 225. 
Commensalism, 335. 
Common lizard (illus.), 193. 
Communal life, 332 ; advantages of, 

333. 
Conurus carolinensis, 228. 
Coots, 222. 

Coral colonies (illus.), 56. 
Coral island (illus.), 57. 
Corals, 55. 
Cormorants, 220. 
Corynolophus reinhardti, 291, 364 

(illus.). 
Corvidce, 231. 
Courtship, 395. 
Crabs, 119; metamorphosis of the 

(illus.), 272. 
Cranes, 222. 
Crayfish, 116 (illus.), 117 ; dissection 

of (illus.), 124: antenna of (illus.), 

380. 
Cricket, 133 ; showing auditory or- 
gan (illus.), 381. 
Crinoids (illus.), 158, 447. 
Crocodiles, 198. 

Crossopterygian fish (illus.), 426. 
Crotalis adamanteus (illus.), 202. 
Crustaceans, 109, 110; larvae of 

(illus.), 346. 
Cuckoos, 227. 
Cucumaria (illus.), 156. 
Culex (illus.), 269. 
Cyanocitta cristata (illus.), 303. 
Cyclops (illus., 112), 111. 
Cyclostomes, 167. 
Cynocephalus maimon, 250. 
Cypselurus (illus.), 297. 

Daddy-long-legs, 145. 

Danaidae, 365. 

Daphnia, 111. 

Death, 278. 

Deep sea-angler (illus.), 291. 

Deep-sea fauna, 446 ; fishes, 447. 

Degeneration through quiescence, 

343 ; through other causes, 348 ; 

immediate causes of, 349. 



452 



ANIMAL STUDIES 



Dentrostoma (illus.), 85. 
Dependence of species, 288. 
Development, first stages in (illus. ), 

256, 257 ; continuity of, 259 ; gas- 

trula stage, 260; divergence of, 

260 ; laws or general facts of, 262 ; 

significance of the facts of, 265. 
Devil-fish (illus.), 105, 106. 
Devonian age, 426. 
Diamond-rattlesnake (illus.), 202. 
Diapheromerafemorata (illus.), 356, 

357. 
Didelphys virginiana (illus.), 239. 
Diemyctylus, 186. 
Diemyctylus torosus (illus), 190. 
Dieotyles torquatus (illus.), 249. 
Digestion of food, 45. 
Diodon hystrix (illus.), 300. 
Diomedea exulans, 220. 
Dipnoi, 170. 
Diptera, 138. 

Dismal Swamp fish (illus.), 173. 
Division of labor, 332. 
Dog family, 248. 
Doves, 225. 
Dragon- flies (illus., 135), 134; eye 

of (illus.), 386 ; compound (illus.), 

386. 
Dryobates pubescens, 228. 
Ducks, 221. 
Duration of life, 275, 

Eagles, 226. 

Earthworms, 72; dissection of (il- 
lus.), 73; circulatory system, 73; 
diagram of kidney (illus.), 74; ex- 
cretion, 74; nervous system, 75; 
egg-laying, 75 ; distribution, 76. 

Echeneididce, 335. 

Echinodermata, 19. 

Echinoderms, 150. 

Eciton, 323. 

Economic entomology, 413. 

Economic zoology, 404. 

Ectopistes migratorins, 225. 

Edentata, 239, 443. 

Edible worm (illus. > 408. 

Eels, 172. 

Egg-laying, 82. 



Eggs of different animals (illus. ), 255 

Maps, 361, 368. 

Embryology, 15. 

Embryonic development (illus. , 257), 
256. 

Embryonic stages of vertebrate ani- 
mals (illus.), 263. 

Emmyclrichthys vulcanus (illus.), 
29S, 299, 355. 

Entomostraca, 110. 

Environment, 395. 

Eohippus, 431. 

Epialtus prodoctus (illus.), 120. 

EpideOa, 64. 

Erenthizon dorsatus, 240. 

Eretmochdys imbricata (illus.), 203 

Ei-gates (illus.), 140. 

Erynnis Manitoba, 436 

Euglena, 25. 

Eumeces, 199. 

Eunice fucata Elders (illus.), 408. 

Eurypelma lentzii (illus.), 146. 

Exoccetus (illus.), 297. 

Fairy-shrimp (illus.), 111. 
Falco sparveritu, 226. 

Fauna and faunal areas, 440 ; of the 

sea, 446. 
Feeding, 391. 
Felis concolor, 24S (illus.), 249, 

F. caffra, 24S. 
Ferae, 246. 

Fiber zibcthicus, 241. 
Fiddler-crab (illus.), 120. 
Fishes, 164; senses of, 178 ; pelagic, 

446. 
Flagellate infusoria (illus.), 26. 
Flatworms (illus.), 60 ; digestive 

system, 61 ; nervous system and 

sense-organs, 62 ; flame-cell of 

(illus.). 62; excretory system, 62; 

parasitic, 63 (illus.), 64. 
Fleas. 138. 
Flicker, 228. 
Flies. 13S. 
Flounder, development of (illus.^ 

274. 
Flying fishes (illus.), 897. 
Food, 4. 



INDEX 



453 



Formation of new races, 405. 
Fossil-bearing rocks and their origin, 

421. 
Fossil brachiopod (illus.), 423. 
Fossils, 420 ; deposition of, 422. 
Foot of the bald eagle (illus. ), 293. 
Fringillidce, 231. 
Frogs, 185. 
Fulica americana, 223. 

Galapagos Islands, 439. 

G aleus zyopterus (illus.), ]69. 

Gall of the white oak (illus.), 30& 

Gallinago delicata, 223. 

Gallinse, 224. 

Gammarus (illus.), 122. 

Ganoidei, 171. 

Garpikes, 171. 

Gasteropods, 89, 97, 10a 

Gastrula (illus., 36), 35. 

Gavia imber, 219, 

Geese, 221. 

Gelasimus (illus.), 120. 

Geographical distribution of ani- 
mals, 435. 

Geological epochs and their animals, 
424 

Geometrid larva (illus.), 356. 

Gephyrea, 84. 

Gerrhouotus scincicauda (illus.), 352. 

Giant water-bug (illus.), 138, 30& 

Gila monster (illus.), 200. 

Glires, 19, 240. 

Gnats, 138. 

Gnawers, 240. 

Golden eagle (illus.), 237. 

Gordius, 69. 

Gorilla, 250 ; (illus.), 253. 

Gorgonia, 56. 

Grapta, 357. 

Grasshopper, 133 ; showing auditory 
organ (illus.), 381. 

Grebes, 217. 

Green leaf insect (illus.), 357. 

Gregarina, 28 (illus.), 29. 

Gregariousness, 328. 

Grouse, 224. 

Gras americana (illus.), 220; Mexi- 
eana, 222. 



Gryllotalpa (illus.), 311. 

Hcematozoa, 30. 

Halictus, 325. 

Halicly stus (illus.), 53. 

Halicetus leucocephalus, 226 ; H. au 

bierlla, 329. 
Harvestmen, 145. 
Hatteria (illus.), 206, 207. 
Hawks, 226. 

Hawkbill turtle (illus.), 203. 
Heliconidao, 365. 
Helix, 98. 
Heloderma suspectum (illus.), 200, 

201, 361. 
Heptacarpus brevirostris, 117. 
Hemiptera, 137. 

Hermit-crabs (illus., 119), 118, 338. 
Herodiones, 222. 
Herons, 222. 
Herring, 172. 
Hirundinidce, 231. 
Hominidce, 253. 
Homo sapiens, 252. 
Homology, 13. 
Honey-bee (illus.), 259, 314 ; (illus.), 

315; posterior leg of (illus.), 316; 

cells containing eggs (illus.), 317; 

hiving a swarm of (illus.), 319. 
Horned toads, 200 (illus.), 208, 297. 
Horse, extinct four-toed (illus.), 

432 ; feet of in fossil pedigree, 433. 
Horse-fly (illus.), 139. 
Horseshoe crab (illus.), 149. 
Horsehair snake, 69. 
House-fly, 138. 
Humming-birds, 229. 
Humpback whale (illus.), 243, 
Hydra, fresh- water, 43 ; (illus.), 44; 

metnods of multiplication, 45. 
Hydractinia, 119 (illus.), 50. 
Hydrodamalis, 419, 
Hydrophilus ( illus.), 311. 
Hydrozoan colonies, different types 

of (illus.), 46, 47. 
Hyla r eg ilia ( illus.), 310. 
Hylobates, 250. 
Hymenoptera, 142. 
Hystrix cristata (illus.), 241. 



454 



ANIMAL STUDIES 



Icerya purchase 288 (illus.), 307. 

Ichneumon fly ( illus.), 343, 844. 

Icteridce, 231. 

Indo- African realm t 443. 

Infusoria, 25. 

hisecta, 110. 

Insectivora, 242. 

Insect destruction, amount of, 414. 

Insect galls on leaf (illus.), 309. 

Insect ravages, prevention of, 414. 

Insects, 130 ; external features, ISO, 
133; internal anatomy, 131 ; res- 
piratory system, 133; communal, 
323 ; parasitic, 341 ; beneficial, 415. 

Instinct and reason, 387. 

Instincts, 389 ; classification of, 390; 
variability of, 398. 

Jpnops, 447. 

Irritability, 387. 

Island faunae, 438. 

Isopods ( illus.),121. 

Itch-mite (illus.), 14a 

Jack-rabbits (illus.), 18. 

Jelly-fish, 47 (illus.), 48, 52; complex 

types of, 49 ; simple eye of (illus. ), 

385. 

Kallima, 357 (illus.), 219. 

Kangaroos, 239 (illus.), 304. 
Katydids, 133. 
Kelp-crab (illus.), 120. 
King-crab, 149. 
Kingfishers, 227. 

Lady-bird beetles (illus.), 361. 

Lamellibranchs, 89 ; sense organs of, 
101, 103. 

Lamellirostres. 221. 

Lampreys, 164, 167 (illus.), 168. 

Lampropettis osceola, 26S. 

Lamp-shells (illus., 86), 87. 

Lancelets, 164, 166. 

Lasiurm borealis, 242. 

Laws of distribution, 437. 

Leaf -eating beetle, antenna of (il- 
lus.), 377. 

Leeches, 80; haunts and habits of, 
81. 



Lemur, 444 ; L. varius, 444 

Lemurian realm, 444. 

Lepas (illus.), 115, 346. 

Lepidoptera, 141. 

Lepomis megalotis (illus.). 176. 

Leporidae, 17. 

Leptoplana (illus.), 60. 

Lerema accius. 436. 

Libeilula pulchella (illus.), 135. 

Life cycle, birth, growth and devel 
opment, and death, 254. 

Light thrown on zoology by paleon- 
tology, 430. 

Limicola;, 223. 

Limulus polyp hemus (illus.), 149. 

Littoral group, 447. 

Living organic matter, 3. 

Lizards, 193, 199; dissection of a 
(illus.), 204. 

Lizzia kozllikeri (illus.), 385. 

Lobsters, 116. 

Locomotion, power of, 2. 

Locusts (illus.), 16. 

Long-eared sunfish (illus.), 176. 

Long-horned borer ullus.), 140. 

Longipennes, 219. 

Loons, 217. 

LopJiius piscatorius, 364. 

Lophortyx calijbrnicus (illus.). 224. 

Lumbricus terrcstris (illus.), 72, 73. 

Lung-fishes, 170. 

Lycosid(P, 306. 

Lymnceua (illus.), 257. 

Lynx canadensis, 248? Z. ru/ws, 248. 

Jfacacus, 250. 

Machrochires. 229. 

Macrobdella (illus.), 80. 

Jfacropns giganteus, 240 ; M. rufus 
(illus.), 304. 

Mad torn (illus.), 298 

Jlalacostraca. 110. 115. 

Male elk (illus.), 313. 

Mammals, four odd-toed (illus.), 15 ; 
general characteristics of, 232 ; 
skeleton, 233 ; digestive system, 
233 ; nervous system and sense 
organs, 234 ; mental qualities. ~3."> ; 
classification, 235; insect-eating 



INDEX 



455 



246. 



2; hoofed, 245; flesh-eating, 



Mammalian age, 426. 

Manatee (illus.), 238. 

Man, 252, 429. 

Man-like mammals, 250. 

Mantis (illus.), 293. 

Marine worms (illus.), 76 ; head of 

(illus.), 77; common (illus.), 78; 

sedentary tube-dwelling (illus.), 

79. 
Marsupialia, 239. 

Mastodon americanus (illus.), 418. 
Mayflies, 134. 

Megaptera versabilis (illus.), 243. 
Megascops asio, 226. 
Melanerpes erythrocephalus, 228 ; 

formicivorus, 229. 
Melanerpes formicivorus bairdii 
Melaftoplus spretus (illus.), 267. 

(illus.), 294. 
Meleagris gallop ava, 225. 
Membracidse (illus.), 367. 
Mesohippus, 431. 
Metamorphosis, 270. 
Metazoa, 22. 
Millipeds, 127. 
Mimicry, 350, 365, 369. 
Mind, 402. . 

Mining-bee, nest of (illus.), 325. 
Miohippus, 431. 
Mnioliltidce, 231. 
Mole cricket (illus.), 311. 
Mollusca, 19. 
Mollusk, auditory organ of (illus.), 

380. 
Mollusks, 89. 
Monarch butterfly (illus.), 141, 268, 

366. 
Monkeys, 250 (illus.), 251, 443. 
Monotremes, 305. 
Morphology, 15. 
Mosquito, 138 ; metamorphosis of 

(illus.), 269 ; head of (illus.), 293 ; 

young stages of (illus.), 312 ; show- 
ing auditory hairs (illus.), 382. 
Mother Carey's chickens, 220. 
Moths, 141. 



Muridae, 17. 

Mus musculus, 241. 

Mussels, 89 ; edible (illus.), 94. 

Mustelidce, 248. 

Myocetes, 250. 

Myriapoda, 110, 127. 

Mysis americana (illus.), 116. 

Mytilus edulis (illus.), 94. 

Nematodes, 67. 

Neotropical realm, 443. 

Nereis (illus.), 76. 

Nerve cells and fibers, 387. 

Nettle-cells (illus.), 44. 

Neuroptera, 135. 

Newts, 186. 

Night-hawk (illus.), 229. 

Nomeus, 336. 

Nomeus gronovii (illus.), 337. 

North temperate realm, 442. 

Nudibranchs (illus., 100), 99. 

Nyctea nyclea, 226. 

Oceanites oceanicus, 220. 
Octopus (illus., 105), 106. 
Onychophora, 109, 127. 
Opossum (illus.), 239. 
Opossum-shrimp (illus.), 116. 
Orange scale of California (illus. ) ; 

347. 
Orchard pests, 413. 
Ornithorhynchus, 237. 
Orohippus, 431. 
Orthoptera, 133. 
Osteosis macrolepidotus (illus.), 

426 
Ostracoderm (illus.), 425. 
Ostriches, 217 ; African or two-toed 

(illus.), 218. 
Ovis canadensis, 246. 
Owls, 226. 
Oxygen, 5. 

Pagurus (illus.), 338. 

Pagurus bernhardns (illus.), 119. 

Paleontology, 15, 424. 

Palinurus, 118. 

Pallas's murres (illus.), 330. 

Palolo worm (illus.), 408. 



456 



ANIMAL STUDIES 



Paludicolae, 222. 

Pandorina (illus.), 33. 

Panthers (illus.), 259. 

Papilionidae, 3G7. 

Parallelism of embryonic stages with 

fossil series, 433. 
Paramcecium aurelia (illus.), 26, 27. 
Parasitic insects, 341. 
Parasitism, 63,335; kinds of, 338; 

simple structure of, 340. 
Parrots, 227. 
Passeres, 230. 
Patagonian realm, 444. 
Pelicans, 220. 
Peneus (illus.), 346. 
Pennatula, 56. 
Percaflavescens (illus.), 165. 
Perching birds, 230. 
Pelicanus erytJirorhynchus (illus.), 

220. 
Peripatus (illus.), 127. 
Per ip at us eiseni (illus.), 127. 
Petrels, 219. 
Pheasants, 224. 
Philhela minor, 223. 
Phrynosoma, 200 ; P. blanivillei, 

(illus.), 297; head of (illus.), 208. 
Phyllium (illus.), 357. 
Phyllopteryx (illus.), 359. 
Physalia, colonial jelly-fish (illus.), 

51, 336. 
Pici, 228. 

Piddock (illus.), 93. 
PieridEe, 367. 

Pigeons. 225; horn-tail (illus.), 344. 
Pike, 173. 
Pill-bugs, 121. 
Pinnotheres, 337. 
Pipe-fish (illus.), 359. 
Pithecanthroptis, 430. 
Planaria (illus.), 60, 61. 
Plankton, 446. 

Platophrys lunatus (illus.), 274. 
Play, 394. 
Plovers, 223. 

Podilymbtis podiceps, 219. 
Pointer dog in the act of pointing 

(illus.), 403. 
Polychaetes. 76, 80. 



Polynoe brevisetosa (illus.), 78L 

Polyzoa, 85. 

Porcellio Icevis (illus.), 121. 

Porcupine (illus.), 241. 

Porcupine fish (illus.), 300. 

Porpoises, 242. 

Portuguese man-of-war (illus., 51 j, 

50; (illus.), 337. 
Prawn (illus.), 117. 
Praying horse (illus.), 293. 
Pribilof group in Bering Sea (illus.) 

330. 
Primates. 250. 
Priorius (illus.), 311. 
Procellaria pelagica, 220. 
Procyon lotor, 247. 
Promethea moth (illus.), 378. 
Protective resemblances, 350, 355, 

368. 
Protohippns, 432. 
Protoplasm, structure of, 10, 
Protozoa. 19. 22, 30. 
Psittaci, 227. 

Pterichyodes milleri (illus.). 425, 
Pterodactyl (illus.). 424. 
Pugettia Hchii (illus.), 120. 
Pulsatina vacuales. 27. 
Puss moth, larva of (illus.), 363. 
Pygopodes, 217 

Quail, 224. 

Rabbits, 241,435. 

Raccoon (illus.), 247. 

Race histories, 41. 

Rails. 222. 

Rainbow trout, head of (illus. ), 3101 

Raja binnrulala (illus.), 305. 

Raptores, 226. 

Ratitae, 217. 

Rats, 438. 

Reason, 398. 

Red squirrel, 19. 

Redi. 70. 

Reflex action, 3S8. 

Regeneration of the tapeworm, 66k 

Remora (illus.). 336. 

Reproduction, 396, 

Reptiles, 192. 



INDEX 



457 



Reptilian age, 426. 
Rhamphorhynchus (illus.), 424. 
Rhizoerinus loxotensis, 447. 
Rhizostoma (illus.), 52. 
Rocky Mountain locust (illus.), 134, 

267. 
Rocky Mountain sheep, 331. 
Rodents, 240. 
Rotatoria, 279. 
Rotifers, 83. 
Ruminants, 245. 

Sabella (illus.), 79. 

Sacculina, 114. 

Sacculina (illus.). 341. 

Salamanders, 184; (illus.), 190. 

Salmo irideus (illus.), 310. 

Salmon, 172. 

Sand-dollar (illus.), 155. 

Sand-fleas (illus.), 122. 

Sandhoppers, 121. 

Sandpipers, 223. 

Sarcoptes scabei (illus.), 148. 

Sargassum, 355. 

Sauba (illus.), 367. 

Sauria, 193. 

Saurian bird (illus), 431 

Scale insect (illus.), 307. 

Scalops aquaticus, 242 ; 8. argen- 
teus, 242. 

Schilbeodes furiosus (illus.), 298. 

Scientific names, 15. 

Sciurus, 17, 19. 

Scorpion (illus.), 144; (illus.), 293. 

Scorpion fish, noki or poisonous (il- 
lus.), 298. 

Scotiaptex cinere.ua, 226. 

Scyphozoa, 51. 

Scyphozoan jelly-fish, development 
of (illus.), 53. 

Sea-anemones (illus.), 54; section of 
(illus.), 55. 

Sea-cow (illus.), 238. 

Sea-cucumbers (illus. 156), 155, 160., 

Sea-lily (illus.), 157. 

Sea-mats, 85. 

Sea squirt (illus.), 162; (illus.), 345. 

Sea-urchins (illus., 154), 151 ; meta- 
morphosis of (illus.), 271. 
30 



Sedimentary rocks, 422. 

Segmented worms, 72. 

Selection, by nature, 284 ; natural, 
287 ; artificial, 287. 

Self-defense, 392. 

Serpentes, 194. 

Serphus (illus. ), 306. 

Serphus dilatatus (illus.), 138. 

Serpula (illus.), 79. 

Shrimps, 116. 

Silurian age, 426. 

Silver-fox (illus.), 248. 

Silver-spot (illus.), 142. 

Simia, 250. 

Simplest animals, life cycle of, 254, 

Sirenia, 239. 

Skates, 169. 

Skin of man, tactile papilla of (il- 
lus.), 374. 

Skinks, 199. 

Slipper animalcule, 26. 

Snakes, 194. 

Snail, 97, 98; marine (illus.), 100; 
tongue rasp of (illus.), 101. 

Snipes, 223. 

Social wasp, nest of (illus.), 328. 

Solaux, 275. 

Soup-fin shark (illus.), 169. 

South American realm, 443. 

Special senses, importance of, 371 ; 
difficulty of the study of, 371 ; of 
the simplest animals, 372; touch, 
373 ; taste, 375 ; smell, 376 ; hear- 
ing, 379 ; sound - making, 382 ; 
sight, 384. 

Species altered by adaptation to new 
conditions, 438; debarred by ina- 
bility to maintain their ground, 
438. 

Species debarred by barriers, 437. 

Speotyto cunicularia, 226. 

Sphenoden punctatus (illus.), 207, 

Sphinx moth (illus.), 362. 

Sphyrapicus car ins, 229. 

Spiders, 145 ; habits of, 146; aggres- 
sive resemblance (illus.), 359. 

Spiny-rayed fishes, 175. 

Spirifer cameratus Morton (illuf,), 
423. 



458 



ANIMAL STUDIES 



Sponges, 33 ; development of the, 35; 
(illus.), 36; distribution of, 36; 
various forms of (illus. ), 38 ; struct- 
ure of, 38; skeleton of, 40; por- 
tion of wall of (illus.), 40. 

Spontaneous generation, 69. 

Squirrels, 15, 241. 

Starfish (illus.), 151; dissection of 
(illus.), 159. 

Steganopodes, 220. 

Sticklebacks, 173. 

Sting-ray (illus.), 299. 

Strix pratincola, 226. 

Strongylocentrotus purpuratus (il- 
lus.), 154. 

Sturgeons, 171. 

Struggle for existence, 281, 283. 

Struthio camelus (illus.), 218. 

Subordinate realms or provinces, 
445. 

Surroundings, influence of, 37. 

Sus scrofa, 246 ; S. indicus, 246. 

Swallow-tail butterfly, chrysalid of 
(illus.), 353. 

Swift (illus.), 193, 229. 

Sword-fish, development of (illus.), 
273. 

Symbiosis, 337. 

Syrphidse, 367. 

Tceniasolium (illus.), 66. 

Tapeworms, 65 (illus.), 66. 

Tarantula-spider (illus.), 146. 

Tardigrada, 279. 

Teleostei, 170. 

Temperature and other conditions, 

6. 
Tenebrio molitor, 28. 
Tentacles, 44. 
Teredo, 92. 

Termites (illus.), 137 ; (illus.), 324. 
Terns, 219. 

Terr apene- Carolina (illus.), 197. 
Thalessa, 342; T. lunator (illus.). 

344. 
Therioplectes, 139. 
Thousand-legs (illua.), 128. 
Threadworms, 67 (illus.), 68. 
Three-toed sloth (illus.), 236. 



Toad, metamorphosis of the (illua.) 
183 ; dissection of (illus.), 188. 

Tomato-worm larva (illus.), 362. 

Trap-door spider (illus.), 147. 

Tree-hopper (illus.), 367. 

Tree-toad lillus.), 310. 

Tremex columba, 342; (illus.), 344. 

Trenatodes, 63. 

Trichechus latirostris (illus.), 238. 

Trichina (illus.), 68, 69. 

Tridacna, 89. 

Trinomial names, 19. 

Trochilus colnbris, 230. 

True fishes, 164. 

Tuatera (illus.), 207. 

Turdidce, 231. 

Turkey-buzzard, 226. 

Turkeys, 224. 

Turtles, 196. 202. 

Tympanuchus americanus, 225. 

Typhlichthys subterraneus (illus.), 
173. 

Tyrannidoe, 231. 

Ungulata, 245. 

Vria lomvia arra (illus.), 330. 
Urocyon cinereo-argentatus, 248. 
Ursus americanus, 246; horribilis, 

246. 
Uiolophus goodei (illus.), 299. 

Vedalia cardinalis t 289. 

Vedalias, 289. 

Vermes, 19. 

Vertebrata, 19, 163, 261. 

Vespa (illus.), 327, 328. 

Vespertilio fuscus, 242. 

Vestigial organs, 312. 

Vorticella (illus.), 27. 

Volvox mi?ior (illus.), 33, 34 ; V. glo- 

bator (illus.), 34. 
Vulpes pennsylvanicus, 248. 

Walking-stick insect (illus.), 356. 
Warning colors, 359. 
Wasps, 142. 

Water-beetle (illus.), 311. 
Whales, 24'2. 
Wheel-animalcules (illus.), 83. 



INDEX 



459 



White ants (fflus., 137), 134. 
White pelicans (illus.), 220. 
Whooping-crane (illus.), 220. 
Wild duck (illus.), 302. 
Wings showing homology and anal- 

ogy (illus.), 14. 
Wood-boring beetle larva (illus.), 

311. 
Woodchuck, 241. 
Woodcock, 223. 
Woodpeckers, 228. 



Worms, 53. 

Xiphias gladiv* (illiu % 258L 

Yellow-jacket (illus.), 327. 
Yellow-perch (illus.), 165. 
Young, number of, 277; care of, 

397. 

Zenaidura macroura, 225. 
Zirphcea crispata (illus.), 93. 
Zoo geography, 435. 



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